Hi,
For a gaming rig I'd pick (and indeed I did, though SB-E wasn't out at the time) a 2500k.
I picked up a 2500k and an ASUS P8Z68-V Pro last year and build a system around that. It's proven to be a great little gaming rig, far far better than I expected.
My friend, always wanting to 1 up me lol, went for the 2600k (+£100) as well as a "better" motherboard - I cannot recall exactly which one it was off the top of my head, but it cost him over £300 vs. my £150. So, he has the higher spec system, yet I'm £250 better off.
Comparing our rigs directly, him with 2x480's and me with 2x570's (the £250 I saved paid for my 2nd 570
and a closed water-loop cooler for the CPU
) there is minimal difference. We both clocked to ~4.8 - having dabbled with 5.0 briefly - hot hot hot lol - before settling on 4.6ghz. Benchmark-wise he pips me slightly in CPU bound ones due to his 2600k having HT. However, when it comes to gaming there no difference. Really, my £100 cheaper CPU performs every bit as well as his - rather chuffed with that I was.
Now, when we bought the 2700k wasn't available, nor were the new SB-E chips. I think a 2700k would be a good buy, it's a very capable CPU, and in theory it's just a higher binned 2600k - so it should OC like a "good" 2600k with 4.5 being hit easily, and 4.8 being achievable with a little more effort. It'd likely do 5.0ghz with adequte cooling, but only really for fun - I'd not 24/7 such an OC personally.
My personal view is that the 2500k is an epic CPU for gaming and it overclocks very well, it's also darn cheap. A 2600k or 2700k is also a great buy, but for pure gaming use I really don't think it gives enough over the 2500k to justify the extra cost. I saved a chunk of cash going with a 2500k and the mid-range (but still quality components and features) ASUS P8Z68-V Pro board and used the money saved to basically DOUBLE my GPU power - enhancing my gaming further. With the one 570 my system was great, adding the 2nd just transformed things - I've got a fairly large post on the forums regarding my SLI experience.
I don't think you'd be disappointed with whatever your purchase, but I feel you can get more system for you money overall by spending smart now. If money isn't an issue then go for it - I too am tempted by a new SB-E 2011 system, despite having
no use for it what so ever over my current rig that does everything I ask of it. But that's the price of being an enthusiast I suppose - still, sensible head wins out in the end for me lol.
Best of luck with whatever you decide
Cheers,
Scoob.