New Buget Build advice would be apreciated

I am selling my powerhouse for a gaming pc to pay rent, but i am already thinking of a budget build to replace it. I am reusing an I5-2500 that i have from a previous build so no cpu is needed atm.

XFX Double D Radeon HD 6850 @ 140
Cool Masters HAF 912 @ $60
Giganyte GA B75M @ $63
OCZ ModXstream Pro 500W @ $70
Corsair Vengence 2 x 4gb @ $41
WD Blue 500Gb @ $70
Asus DRW 24x dvd Burner @ $20

Total: 464 + tax

I want to keep this case because i know it is easy to keep it cool and I have used the 922 before so I am hoping the 912 is of similar quality. I mainly want to try to keep 40ish FPS in BF3 on min settings on a 1680x1050 resolution. My main concern is the psu and mobo. I want to try to keep upgradability in mind but i can find any better psu or mobo that would not increase my budget by too much more. My max budget would be about $600ish. But id reall like to keep it at $500. IF anyone can offer any suggest to improve this build without increasing the cost to much would be greatly appreciated. FYI all these preices are from Newegg and I live in the usa.