I know if you have a bad cpu and a great video card you will be bottlenecked thus you will only get a fraction of the video cards full power. My question is would you see an improvement if you have say... a pentium d 2.8 paired with a 8800 gtx over a pentium d 2.8 paired with a 1950pro. Not everyone can afford to buy all parts at once I am just wondering what percentage increase if any would occur.
Trade the pentium d for a core 2 duo. Although pentium ds are duel core, they're not as efficient as C2Ds, and therefore would go better with a 8800GTX. If you keep the PD, then the x1950 would be a good choice.
Agreed, a D820/D920/D915 isn't going to be sufficient to keep up with an 8800GTX. Go with the X1950 Pro. If you can upgrade your CPU to a Core 2 Duo, even a low end one like an E4500, then you could use an 8800GTX.