Need an upgrade? Can't afford top of the range? Neither can most people... the sensible people at least. Mainstream cards can still provide good performance without breaking the bank. Of course, you knew that already, so let's cut to the chase. Hardocp review a PowerColor X700:
The PowerColor Bravo X700 256MB video card may not show any improvement with a 256MB framebuffer versus a 128MB framebuffer in games, but at least it won’t break the bank and does seem to perform faster overall than a GeForce 6600. Keep in mind the X700 runs with a 400MHz core frequency while the GeForce 6600 runs with a 300MHz core frequency, so the X700 does have a higher raw fillrate. Therefore, the larger framebuffer may not make any difference, but this video card did provide a better gaming experience than the GeForce 6600.
[The review]