Corsair 850TX might work but don't bet on it, XFX 850W Pro Core will work I think. Otherwise you'd be looking into much higher power PSUs, and terrible value for money. I'd suggest staying with the PSU you have now, and getting a cheap additional 400W to power two cards. Unless of course you're looking to expand operations in the near future and would like to keep your current psu for that, then go for the XFX. Here in Europe its about 100 euros, I think I saw it on Newegg for 139.99 at some point.