I have a GeForce 8800 GTS 320 MB video card. That should be rather common I guess.
8600GS, here (512 dedicated). Many disabled could be turned back on with this specific card since the Dual_CPU system can coordinate the extra resources at a reasonably fast rate.
DA still runs a tiny bit faster than on the earlier PC (6200AGP) and i couldn't really detect that much of a difference for DL.
What truly gained a noticeable speed is when bigger maps are played all the way through the end; the HUGE amounts of activity makes for cpu intensive rendering which are handled quite well. GPUs will always provide support for precision and enhanced texturing, no matter how new or 'better' while the main system CPU must takes care of plenty.
TA is an entirely new experience though, and is in fact waaaaaayyyyy faster than DA -- that is, with high-end video gears or not.
Don't worry though, your 8800 is again a LOT more powerful than the 8600 i have.