Help on new build please

I don't see much to improve upon. Looks like pretty good quality components you've chosen and a good balance between processor and GPU. Only thing I might change would be the case as I prefer cases with a bottom mount PSU and modular PSUs, but that's kinda a personal thing. That GIGABYTE card looks badass BTW.
 
If you play demanding games the GPUs the single most important component. The 5850 is a significant step down from the 5870. Charts here. Your choice.
 
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