Nope. The G70's architecture has a maximum of 24 pixel pipelines and 8 vertex shaders, so if you have the 7800 GTX all you can do is overclock it.
The X700 is decent if you compare it to the 6600 GT. I think the X700 XT has 8 pixel pipelines and 6 vertex shaders, but since the XT variant is so rare, I assume you have the Pro variant, which should have 4 pixel pipelines and 6 vertex shaders. It might be possible to unlock them, but I've never tried it since I use nVIDIA (I might try out the X1800 XT though