I got a new card a while ago. (radeon 9600pro 256 mb) It gives an increase of about 10fps if the settings are the same as earlier (but I'm picky so I cranked on the pixel shaders and the antialiasing)
You should try it on my comp- 2gb of ram, a raid driver, two 160gb hard disks, a pentium 4 and a gforse fx video card, a sweet system and i know rct3 soaked will not cause me any trouble. But i have lost intrest in rct3 and diverted back to no limits
Good ram, don't know about the raid driver, ok processor, ok video card. I don't see why you need so much ram though. Why not post more about it, like what gf fx card you have, or the processor speed?
Anyways, if I upgrade my comp again, it'll be ram next (I have 512, want 1.5 gigs), then I might consider a faster amd athlon processor (I heard they are better than the intels, though a bit less reliable)