I just had a quick browse on the the OcUK forums and it seems that the X1950XTX scores in some benchmark tests better than the 8600GTS which I found odd but I can't find recent benchies for that card and I don't know if they are reliable.

I can safely say a total entry level 8800GTS is the best card you coudl have if you put that extra £30 in. For the performance, it really REALLY is worth it. the gaming would be absolutely amazing.