Corsair GS700 only 80% efficiently, pure output only 560W more less.. Your VGA 7850 consume 150-175W, if you crosfire, theoritically from web amd : http://www.amd.com/US/PRODUCTS/DESKTOP/GRAPHICS/7000/7850/Pages/radeon-7850.aspx#2, recommend minimum 600w & 8gb ram.. to avoid bottleneck, you shall upgrade your psu to minimum 800W 80+ pure bronze certified psu or greater ( mine using Corsair HX850W, 90% efficiency with 2 SLI Msi GTX660Ti Power Edition/OC, each use 150W)