rFactor runs well on any modern system - of course, the better it is, the more you get out of it. So bare in mind that the really good screenshots here will probably be with everything turned to the max.
For an idea, my system is a dual core @ 3.2Ghz, 4Gb RAM and a 8800GT and I can run all of the settings on max, 8x Anti Aliasing and still get great framerates - I have vsync turned on so never go above 75fps anyway..