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The i7-3820 is going to be about £260 apparently, which isn't much more expensive than the i7-2600k. The motherboards are quite a bit more expensive, but you get an upgrade path to Ivy Bridge E. Other than PCI-E 3.0 slots, you can also get 8 DIMM slots, making it cheaper to get to 32GB if you want. For gaming though, the RAM issue is pretty much irrelevant. I guess you have to decide for yourself if the premium for PCI-E 3.0 and quad channel memory is worth paying. A tough call to makeThere is always the 3820 quad core which is due out very soon, then you can have x79 a bit cheaper
For gaming i'd grab the 2600k and the 7970; cheapest yet most effective.
The processor won't bottleneck or anything.