I'm looking at the specs on two different CPUs and I can't decide which makes better sense.
I'm not planning to overclock, so that is not a consideration. I will install video cards, so the onboard video is not a consideration. Cake is a consideration...
Sandy Bridge Intel Core i7-3820 supports only PCI-e 2.0. memory bandwidth is 51.2GB/s and DMI bandwidth (graphics?) is 5GT/s. Cache is 10MB. CPU frequency is 3.6Ghz
Ivy Bridge Intel Core i7-3770 (or the 3770K for a few dollars more) Third gen Core, so less power, and it offers PCI-e 3.0. Memory speeds are the same, memory bandwidth is half that of the previous processor at 25.6 GB/s, cache is 8Mb and DMI bandwidth is the same as the previous. CPU frequency is 3.4Ghz
The performance benchmarks all show the 3770 higher than the 3820.
I don't get it, does the higher speeds and feeds not make it outperform the 3770? What reasons can there be to get the 3820 over the 3770?
And then, of course if I get the 3770, I may as well fork over the $30 extra for the K-model and if I ever want to overclock, I can, right?
Generally speaking, Ivy Bridge CPUs are on average 6% faster than Sandy Bridge CPUs; assuming the same clockspeed. Perhaps in the single or few benchmarks you've seen Ivy Bridge performs better than that.
The major improvement is the graphics core the Intel HD 4000/2500 have pretty significant improvement over Sandy Bridge's HD 3000/2000. But that is more or less meaningless for anyone looking to install a graphics card.
Which one should you buy? I would just get the Core i7-3770. Should you spend more for the "K" model? The sensible answer is yes since it is only $30 more. You don't need to overclock immediately and getting a "K" model is kinda like future proofing you PC a little bit. When you decide that a stock speed i7-3770k is not longer fast enough for your needs, then you can simply overclock it. Otherwise, you need to build a new PC. Guess which one is cheaper... You do need to buy a new heatsink capable of cooling an overclocked CPU.
PCI-e 3.0 basically has 2x the bandwidth of PCI-e 2.0. However, you will probably have to wait GPU generations before the very highend graphic cards will begin to become a bit bottled by PCI-e 2.0. For example, I would say that the very high end Radeon HD 9950/9970 will be bottlenecked a bit by PCI-e 2.0 (whenever they are released). However, the slower Radeon HD 9850/9870 probably will not be bottlenecked by PCI-e 2.0. If you are the type of person who spend several hundreds of $$$ for the highest end cards or two very high end cards for SLI or XFire, then the recommendation would be to go with PCI-e 3.0... meaning Ivy Bridge.
Note that games do not use Hyper Threading, so if this is a purely gaming PC, then you are more or less wasting money on a very good / excellent CPU with Hyper Threading (HT) capabilities. It would be better to save money and go with the Core i5-3570k.
Socket 1155 (Ivy Bridge and Sandy Bridge) is basically dead. No new CPUs will be released for that socket... or at least nothing that will rival a Core i5-3570k and Core i7-3770k. Haswell is coming in June and it is socket 1150.
Socket 2011 will still have a bit of life left in it. Ivy Bridge-E will be coming out this year so that socket will continue to live. Is it better to get Ivy Bridge-E vs. Haswell? I can't really answer that other than to say if you need a 6 core Intel CPU and you are willing to spending a lot of money. then the answer will probably be sure...
Ivy Bridge-E will support PCI-e 3.0 as long as you buy a socket 2011 motherboard that has a PCI-e 3.0 slot.