So the thing is, I have a Core 2 Duo E7500 and XFX Radeon HD 5830 (the RAM isn't the problem right now).
I have some money for an upgrade - not that much, though -, and I was thinking a modest ASUS P8H61-M LE motherboard + Core i7 2600k should do it.
But then I started to compare it all - the purpose of all this is gaming, by the way -, should I upgrade the C2D E7500 to a i7 2600k, or should I replace the HD 5830 for a HD 6950?
You would probably get the most bang for your buck out of the GPU upgrade for gaming. That is a very nice processor though and you can overclock it pretty easy if that is your thing. The problem is if you get a high end GPU then your CPU could be slowing down your GPU. A CPU change will help your GPU run faster but there is only so much a CPU can do to help a GPU.