Bigger numbers are always better, right?
The 7970 is bigger than the 7870, and it is better. 8GB of RAM is bigger than 1GB, and it is better. Naturally, one would expect the i7-3820 to perform better than the i7-3770K, since it is also has a bigger number. Let us take a closer look.
Image: The contenders. Image courtesy of newegg
The i7-3820 supports quad-channel RAM, and has 40 PCIe lanes, meaning it can support 3 or even 4 graphics cards, and most importantly, it is expected to perform better while maintaining the same total platform price as the i7-3770K. The i7-3820 also has slightly more L3 cache and a higher clock speed, and can handle 64GB of RAM to the i7-3770's 32GB. The i7-3820 can later be upgraded to an i7-3930K or i7-3960X, whereas the i7-3770K is the end of the line for its socket.
Let us address the issues one by one.
First, quad-channel RAM. We have seen this before during the X58 days, but some people really think that having RAM in triple-channel (or quad-channel with X79) is going to make a significant difference in power/speed. It will not do so. Multi-channel RAM is intended to remove any RAM bottlenecks, and with modern DDR3 RAM, there is little to no bottleneck. Multi-channel RAM does not boost your CPU/GPU or anything else, it simply provides more bandwidth. If your RAM data transfer rates were not a bottleneck before, then using a multi-channel RAM configuration is not going to do anything.
You can see this in LegitReviews DDR3 X79 Performance Review, TweakTown's X79 Memory Analysis, and Tom's Hardware article on parallel processing. In real programs, dual-channel or quad-channel makes no difference. Even in most synthetic benchmarks you will see no meaningful difference, with the exception of SiSoft Sandra. Unless you have a specific need for extreme memory bandwidth, you will see no difference from going to triple or quad channel.
Image: Little difference between dual and quad-channel RAM. Image courtesy of LegitReviews
What about having more PCIe lanes? With your typical Z77 motherboards, you will be running one card on x16, or two cards at x8/x8. The exception is the very high-end motherboards with an extra chip that allows up to four cards. With the i7-3820, you can have 2 cards at x16/x16, or up to 4 cards at x8/x8/x8/x8. If you really need to have 3 or more graphics cards, then we agree that X79 is probably the way to go. However, as you can see Techpowerup's GTX 680 SLI Review, Guru3D's GTX 680 SLI review, TechPowerUp's HD 7970 CrossFire review, and Guru3D's HD 7970 CrossFire review, two high-end cards are enough to run even the most demanding games at 1080p, which means that X79 is not needed for anyone gaming below 2560x1600. According to Steam's hardware survey, roughly 0.8% of gamers have a screen with a resolution above 1920x1200, and according to PCGamer, roughly 0.2% use more than one screen. For the other 99%, two high-end cards are definitely more than enough.
"But even with two cards, don't we need them both on x16/x16, rather than x8/x8?"
Image: PCIe scaling. Less than 1FPS difference between PCIe 2.0 x8/x8, PCIe 2.0 x16/x16, PCIe 3.0 x8/x8, and PCIe 3.0 x16.x16, even with flagship cards. Image courtesy of behardware
The answer, as shown in Anandtech's exploration of HD 7970 PCI-E bandwidth and Techpowerup's Ivy Bridge PCI-E scaling article, is that the difference between x8 and x16 is about 1-2 FPS at most, and more often than not, there is no difference.
Image: PCIe scaling. Less than 1FPS difference between x8 and x16, even with flagship cards at high resolutions. Image courtesy of TechPowerup
Even with multiple cards at high resolutions, there is still no difference between x8/x8 and x16/x16, as seen in HardOCP's analysis of x16/x16 vs. x8/x8 and Tomshardware article on CrossFire And SLI
Image: Less than 1FPS difference between x8 and x16. Image courtesy of Anandtech
For users on standard resolutions, x8/x8 vs x16/x16 is not going to make a difference in performance. Even with a 680 or a 7970, or two 7970's or even with three or four 7970's, PCIe bandwidth is not a bottleneck. Anand's conclusion on this matter is very solid:
"...in fact this may be the greatest benefit of PCIe 3 right now, as it should provide enough bandwidth to make an x8/x8 configuration every bit as fast as an x16/x16 configuration, allowing for maximum GPU performance with Intelís mainstream CPUs." [source, emphasis added]
So now we are down to the most important issue: Performance. The i7-3820 is using a higher chipset, a higher-end socket, it has more cache, and is derived from higher-end silicon (the same that gave us the $1000 i7-3960X). Even if it is a quad-core, just like the i7-3770K, it ought to perform better... right?
Sandy Bridge was released in January 2011, and Ivy Bridge was released in April 2012. Ivy Bridge brought about a small improvement in IPC (Instructions per clock), giving it somewhere between 5%-10% better performance over Sandy Bridge. This improvement is small, but it is consistent. Ivy Bridge is also built on a new, more advanced manufacturing process node. Intel uses a 22nm process and 3D-transistors, both of which contribute to increasing speed for the same amount of power use.
If you want a great overview of how the two perform, Anandtech's Bench tool is always extremely useful: Bench i7-3820 (Blue) vs i7-3770K (Dark Gray)
Out of the 52 office benchmarks, productivity benchmarks, content creation benchmarks, multi-threaded benchmarks, single-threaded benchmarks, power consumption benchmarks and gaming benchmarks that Anandtech compares, the i7-3770K wins . . . all 52 benchmarks.
Image: i7-3770K beating i7-3820 by a small margin in Sysmark. Image courtesy of Anandtech
And the others agree: Anandtech's full review, as well as Hot Hardware's review, Guru3d's review, and Legion Hardware's review, the i7-3770K outperforms the i7-3820 in almost everything!
Image: i7-3770K beating i7-3820 by a small margin in video transcoding. Image courtesy of Guru3d
Performance in normal software, performance in games, performance in synthetic benchmarks, the i7-3770K will do better than the i7 3820 in all of them. In fact, even if you swap the $300 i7-3830 for a $550 i7-3930K, the i7-3770K will still win nearly twice as many benches, as shown Anandtech's direct comparison. The next step up from the i7-3770K is not an i7-3820 or an i7-3930K, it is the i7-3960X, which is undeniably the better CPU.
Image: DAWBench results from ADK Pro Audio
While the i7-3770K wins most benches, it is still not 100%. One place where the i7-3820 does make sense is for a few specific non-gaming applications. For example, it performs better in some digital audio processing software, as seen above. If it is critical for your system to support VT-d (you should know if you need it), then the i7-3820 makes more sense.
Image: This is what most performance graphs will show, the i7-3820 trailing the i7-3770K. Image courtesy of hothardware
We advise people to go for performance/price, whenever possible. After seeing performance, let us look at platform price. The total platform price is typically said to be the same, since the X79 motherboards are typically more expensive, while the i7 3770K is more expensive by $30. Please note that the cheapest X79 motherboards (at the time of writing) start at ~$200, which is the price of premium Z77 boards, and there are many quality Z77 motherboards that are significantly cheaper than the cheapest X79 boards. The 3830 has a 130W TDP, and comes without a stock cooler, so you are forced to buy an aftermarket HSF, and it needs to be a beefier one than what you would use for a 3770K, which cancels out the difference in CPU price. Thus if price is an issue, then it is in the 3770K's favour, as you can get the platform for cheaper, or get premium products for the same platform price as the 3820. Unless you can get the i7-3820 with a steep discount, then the i7-3770K has better performance/price, since it has better performance, and similar or lower price.
One reason to get the i7-3820 is to be able to upgrade to an i7-3930K or i7-3960X later. Thus you are buying the i7-3820 as a temporary solution. This is wasteful, as you are spending $300 on a CPU you do not intend to use for long. It is also a gamble. By the time you can afford the $600/$1000 for an upgrade, something better might be on the market (Haswell?). Future-proofing attempts are usually a waste of money. It is always best to buy the best item in your budget, instead of trying to future-proof your PC.
Even though both points are in the i7-3770K's favour, these are minor issues. The i7-3820 will consume more power and run hotter, but not by much.
Before we conclude, let us address a minor issue: It is tempting to say: "Are you telling us that Intel made a product for which there are no customers? You think you know better than Intel?" No. Intel knows that there is a very small number of customers who need more than 2 graphics cards but cannot afford $1000 for the CPU, and Intel also knows that there is a very large number of people who will buy whatever has the biggest number and fits the budget. Anand put it perfectly before Ivy Bridge was even out:
"The 3820 admittedly targets a niche, but it does so without any real trade offs. If you land outside of the 3820's niche however, you're better served by the 2500/2600K at a lower total platform cost or a 3930K/3960X if you're running a heavily threaded workload and can use the extra cores." [source, emphasis added]
With the i7-3770K now available, that niche which the i7-3820 serves is reduced. Most people buying the i7-3820 are not buying it for handling 3 or 4 graphics cards; they mistakenly think it is a better CPU than the i7-3770K.
No. The i7-3820 is a good CPU. In fact, it is an excellent CPU! However, now that Ivy Bridge is out, the i7-3770K is the better CPU. While it may not perform significantly higher than the i7-3820, it does consistently perform better, usually performing 5%-10 better. Normally, the difference in price between the two is roughly $20-$30, so it makes sense to get the better performing i7-3770K. In the rare situation that the i7-3820 has a major price cut or combo, but there is no price cut or combo for the i7-3770K, then it makes perfect sense to go for the i7-3820. Our conclusion below applies to normal situations, where the i7-3820 is an excellent CPU for its price, but the i7-3770K is 5%-10% better while still the same (or even cheaper) platform price.
99% of gamers are fine with one or two high-end graphics cards. The only reason to go with the i7-3820 is if you meet these criteria:
The i7-3820 has a bigger number in its name, a bigger number for its socket and a bigger number for the chipset it uses. If that is what you want, go for it. The i7-3770K has better performance. Which matters more to you?
For ~$300, the best CPU is the i7-3770K. The next step up is the i7-3960X. For gaming, there is no logical CPU in between.
We recommend builds for all budgets at Logical Increments. You'll find the i7-3770K at the high end of our recommended builds at Logical Increments, but not the i7-3820.