Well, I own the HIS Excalibur edition of the X1950 (which if I remember is slightly clocked faster from factory than the other models, but hardly by enough to make a huge difference) and although many people mock the card it actually performs rather well for me. It'll run games such as CS:S HL:2, Battlefield 2, the new Tomb Raider Anniversary all on high details with full AA and AF enabled. It also runs Battlefield 2142 on medium to High detail smoothly. I'm not sure if it's one of the best DX9 cards out today but for what you pay for it, it does it's job and quite sufficiently.
It runs Company of Heroes, Need for Speed: Carbon and the new Command & Conquer on full detail at a high resolution too with no hiccups.
I'm not sure how much of a difference, if any, you would experience going from your 7900GS to an X1950 though.
Rove.