I asked Esreality what I should upgrade using a low budget (300 - 400 pounds) with what was my current hardware:

3.0ghz Core 2 Duo
4gb DDR2 Ram
Radeon 4870 1gb
Normal mobo and drives

I was considering getting a new 3d card (6870 most likely) but you guys correctly said that I should rather upgrade my processor.

I first waited a little, as my pc still ran most games pretty well, however I couldn't get rage to run well at all... as in over 60fps (I really can't play at such a low frame rate...) So I promptly ordered the following hardware:

Intel i5-2500 (Non K)
generic intel mobo
8gb DDR3

This came to about 300 pounds in SA (Things are more expensive here) However the performance difference has been huge.

I now run everything at max, and although I haven't really checked the frame rates they must be around 100 in most games (on a 120hz monitor). Even Rage is running so smoothly, it's like wonderful latex surfaces covered in strawberry flavoured lubricant.

So thank you for the good advice. The process of the upgrade was also quite educational, as I never knew that processors had gotten so much better in such a short space of time. It appears that even the sandy bridge celeron is faster than my old CPU. Not going to bother upgrading my 3d card now, as there is no point.