Better CPU = More FPS?

Hello all,

Basically, I've just bought an MSI HD 4830 OC edition, hoping it would improve fps in games.
Would getting a better CPU, say for example an AMD64 X2 3.0GHz, have a BIG effect on fps?

I've read benchmarks for the 4830, and in games like COD4 it gets around 100 fps @ 1280 x 1024 (my res)
The only this is the benchmarks for that are with really uber cpu's and ram e.t.c.

With this system, what difference in fps would I get @ COD4 compared to these benchmarks - http://www.legitreviews.com/article/838/5/

AMD64 X2 2.0GHz

2GB 533MHz RAM

320GB HDD

MSI HD 4830 OC

Windows 7 64-bit

ASUS A8BN-MR

I mean, say I ran COD4 now and I got like 80 fps, if I got a AMD X2 3.0GHz would my fps suddenly shoot up to like 100+?

Thanks.

I'm afraid my mobo doesn't support it as it came with my HP pc