Looking to upgrade my 7900gtx. I have a core 2 duo e6700, 4gig ddr2 800 OCZ ram, 600 w power supply, Lexa nxzt case and a 22' LG widescreen LCD monitor. Do I really nead a 8800gtx or will the 8800gts or 2900xt do, which should I go for. Thanks in advance for your comments and suggestions.