Well for mostly gaming the the i5 2500K is all you need, the i7 2600K has Hyperthreading and a little more cache onboard, none of these things affect game performance,
http://www.anandtech.com/bench/Product/288?vs=287
You can see the gaming tests at the bottom.
So you can save a bundle of money,
Your basketProduct Name Qty Price Line Total
Intel Core i5-2500K 3.30GHz (Sandybridge) Socket LGA1155 Processor - OEM £155.99
(£129.99) £155.99
(£129.99)
Asrock Z68 Extreme4 Intel Z68 (Socket 1155) DDR3 Motherboard £144.98
(£120.82) £144.98
(£120.82)
Corsair XMS3 4GB (2x2GB) DDR3 PC3-12800C9 1600MHz Dual Channel Kit (CMX4GX3M2A1600C9) £33.59
(£27.99) £33.59
(£27.99)
Cooler Master Hyper 212 Plus CPU Cooler (Socket AM2/AM2+/AM3/775/1155/1156/1366) £19.99
(£16.66) £19.99
(£16.66)
Sub Total : £295.46
Shipping cost assumes delivery to UK Mainland with:
DPD Next Day Parcel
(This can be changed during checkout) Shipping : £9.00
VAT is being charged at 20.00% VAT : £60.89
Total : £365.35
Or save £20 more by keeping your existing heatsink and just gettting some new thermal paste to re-fit it.