There were prototype fx5900's, but the fx5600 is the best actually made and sold IIRC(if you can still find any, they're getting rare), but the best commonly available pci cards is the fx5700le followed by fx5500 and the fx5200 and ati 9250. An ati 9100(better than 9250) fits in there somewhere between 5700le and 5200, but don't know for sure.