So I am putting together a rig with a high-end MSI mobo, 8 gigs of G-Skill RAM @ 1866 MHz, an i3 2120, an OCZ Agility 60GB SATA III boot drive, a Corsair AX850W PSU, and a Gigabyte Ultra Durable VGA Series AMD Radeon HD 6850. The GPU will be changed out for a 7990 when it comes out, and the i5 2500k equivalent of the Ivy Bridge line-up. I was wondering if once I got the 7990, could I Crossfire it with my 6850? Thanks.