I just went to an i7 930 from a Q9450 and I can tell I was very much bottlenecked with just a single 5870. Clock per clock the i7s are just better and overall I think they overclock better, especially when compared to a processor on the 750i chipset maybe not so much P45. It would probably be a real challenge to get it to 4.2 ghz. 1920x1200 seems to be very much a resolution that is on the borderline of graphic and processing needs. It depends which application you're running whether or not you'll be CPU bottlenecked, but overall I think you will be.
But put it this way I'm liking core i7 and x58 and not missing nvidia chipset motherboards at all