Hi
I have just bought one of these psu in mint condition for £120.
http://www.overclockers.co.uk/showproduct.php?prodid=CA-041-OC&groupid=701&catid=123&subcat=1098
Should power 2 gtx 480s in sli dont you think.
Max power usage for a single GTX480 is around 320watt so double that for your graphics cards, add the rest of your system and factor in about %10-15 redundancy.