If your main use is gaming, you could probably just go with an AMD build. You can save money by bumping that X6 processsor to an X4. The X4 works better than the X6 in games. Secondly, you don't really need a 1000w PSU. A 750 or 850w (depending on whether you'll crossfire and OC) will suffice.
With those changes, you could bump the GPU in your AMD build to a 5870 and you'll be good to go.