Advice for my first gaming rig

I have put together a list of components here:

Motherboard: MSI P67A-GD55 (B3) LGA 1155 Intel P67 SATA 6Gb/s USB 3.0 ATX Intel Motherboard

Memory: CORSAIR DOMINATOR GT 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 2133 Desktop Memory Model CMT4GX3M2A2133C9

CPU: Intel Core i5-2500K Sandy Bridge 3.3GHz (3.7GHz Turbo Boost) 4 x 256KB L2 Cache 6MB L3 Cache LGA 1155 95W Quad-Core Desktop Processor BX80623I52500K

Power Supply: CORSAIR Enthusiast Series TX650 V2 650W ATX12V v2.31/ EPS12V v2.92 80 PLUS BRONZE Certified Active PFC High Performance Power Supply

After Market Cooler: CORSAIR CWCH60 Hydro Series H60 High Performance Liquid CPU Cooler

The hard drive, case (including fans), and OS will be recycled from my former pc build.

My GPU of choice is the Radeon HD 6950 2GB, but I am unsure of which version to buy. I plan to mod (and possibly OC) the card into a 6970, but I cannot tell which are reference cards and which are not, and would like some help in deciding which version (MSI, XFX, HIS, etc) and model to buy. You've most likely already figured it out, but I also plan to OC the CPU.

I have done a quite a bit of researching on how to build a new PC from scratch, but only a little bit of time has been spent actually building anything.

Does anyone have advice, criticism, or recommendations on any of this? Since this is my first build time building a PC completely from scratch, I figure that I've probably messed *something up, and/or overlooked something..