Sandy Bridge vs Ivy Bridge and PCI-e 2.0 vs 3.0

What are you going to be doing with your PC?

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.