So I put together a pc last year and here are the specs. 6 gigs ddr3, i7 920 2.8 gig with water cooling, 1.5 tb hard drive and a ATI xfx 5870 video card. Now I am looking to make an upgrade however i'm not sure what would be the best for around 300~ dollars. Any help on this would be great, such as what other video card could I crossfire or if I should get more ram. Thanks guys!