I run my system on an xtech 350Watt smps. Now I want to change my graphics card from 6600gt to 7900gt. This smps I have supplies only 12A on the 12V rail, it seems. The nvidia site asks me to get a 500-600W smps with 30A on the 12V rail, while a review site (anandtech or pcstats?) says 20A on...