Deciding on new video card need help.

Hello my computer is a gutted Alienware Aurora from 2004 era. It has Asus SK8V mobo, socket 940, Athlon 64 FX-53,150 GB 10,000 Rpm. Raptor as main hard drive and 500 GB Seagate as back-up drive, 4 GB corsair regestered ram, a pair of Samsung DVD/CD burners, Alienware 480 watt power supply. Ultra all in one media card floppy drive. ATI Radeon X1650 Pro 512 MB video card,Zalman 9500 CPU cooler,Zalman VF-900 VGA cooler, All stuffed in a SilverStone KL02 case. Ok what would be the best of the best video card for this older AGP mother board ? I like to play games the computer plays GRID and other games very very well. I want the very best with out having to replace everything I worked hard for. I was thinking of Sapphire 3850 video card. Any help would be appreciated. :confused