I admit I'm a bit behind in terms of hardware
(though I have the same graphics card as you) but I remember the period when I had the 4850 and only a single-core Celeron 4 with it, and the problem I had with several games was that I could run them on any resolution and details settings I pleased, but unfortunately the FPS were low on every setting and it didn't matter if I'm on 1280x1024 and uber-high details or 640x480 and everything set to lowest. If the processor is very good, then it can be something else, but if graphics settings have no influence, then it cannot be the graphics card.