I believe your computer system (you should specify what CPU and GPU you are talking about; cuz I think you've already confused Raa) is holding up much of your performance in FSO. Your GeForce 4 Ti is ... not enough to stomach what FSO can throw at it, so I suggest finding a better video card overall is a better idea, rather than trying to balance CPU and GPU speeds. Both are equally important as if you don't have a fast CPU, there's no point in having a lot of space in which to transfer data (GPU). And if you have a fast CPU, it's made pointless because your GPU will be clogged with more data than it can hold because it's too small.
Personally, I use a GeForce FX 5600 AGP 8x 256 Mb. Most cards won't run without that AGP, and it's either 4x or 8x. Then you've got to choose between 128 or 256 Mb, usually. So, if you're lookin' for value, just get my card with your new system, unless you want that extra punch...get a newer one.