I like the 2630 a lot and it's a nice improvement over the the Clarksdale Quads because of the hyperthreading. The 2630QM compares favorably to the I7-950, 960, and the 2500k. My wife has a notebook with the i-7 2670 QM stepped to 2.2ghz and i think it's a small upgrade honestly. I believe your chip consumes 45watts? and can go up to 2.7-2.9ghz? I might have to look that up.
Yes. the benchmarks between the 2500k, 2600k, and 2700k to the 3550, 3570, 3770 are minimal at best. Is 4-10% really worth buying a mobo, cpu if you already own the 2500k-2700k? Absolutely not. Buy a new GTX 670 or 680 and your 1155 system is off to the races. The 670 has shown a 25%-34% improvement over the GTX 570 in most cases. That would trump a CPU upgrade imo. Those differences can also easily be achieved with some mild overclocking. Now if your in the market for a new system by all the means go for the newest technology and go the 2011 cpu route.
My rig is a I5-750 Lynnfield (1156 chip) 2.66 default OCed to 4.04 on a Gigabyte P55M-UD4. I could go higher but it's overkill for todays games. I have two GTX 470s in SLI and can play anything out there with high-enthusiast quality. I'm waiting for Nvidia to sort out the artifacting problem with the GTX 670s and then I am going to upgrade with two of those badboys.