I ran my 256MB x1900gt for a while but didn't like how much it slowed down my whole system, even for just general use browsing & such.
The card also ran HOT, consistently 85-90C; it would heat to 90C, fan would kick up a notch (loudly), cool down to 85C, then start the cycle over again.
I would get about 330ppd. Compared to about 250ppd with my C2D and the graphical client (can't get the console smp version to work for some reason--comments?) with no heat issues. I went back to the standard version and whole system breathed a sigh of relief.