I'd keep a GTX.
But, it depends really - what resolution do you game at?
There's not a huge amount of performance difference at lower resolutions/lower AA levels, but there can be a massive performance difference at higher resolutions/higher AA.
Here's an example:
We did a 3D Graphics test using "rthdribl" on a 26" Samsung Panel (1920x1200) with x16AA.
We ran the following rig with a 8800GTX and then an 8800GT:
Q6600 Overclocked at 3.4Ghz
2GB Crucial DDR2 PC8500 RAM
Abit IP35 Pro Motherboard
500GB WD SATA
rthdribl Skull Demo
Average FPS 8800GT: 5FPS
Average FPS 8800GTX: 35FPS
Big difference between the two. The GTX is still the daddy (barring the new GX2s) and although you're unlikely to game with such high levels of AA, I'd still recommend keeping your GTX.
Originally Posted by name='firefly'
My feeling is to go with a GTX on the p35 board and sell the rest.
I'd agree with this.