From what I've experienced, I don't think the heavy graphics cards really thrive until you give them high resolutions. The question is, does 1680×1050 count as "high". I don't really know. But hear me out:
I have a 7900 GTX, and just upgraded from a 1024×768 CRT to a 1920×1200 TFT (the BenQ FP241W). Having changed nothing else about my system, and noting that the weak link remaining is actually the CPU (A64 3000+... it only didn't become a 4000+ at the same time I got my monitor because I really, really hate re-installing CPU heatsinks), I was surprised to find that my framerates at the higher resolution actually went up.
Particularly it seems to prefer antialiasing a lot more than it did. I don't quite get why exactly (performance staying the same because of the CPU bottleneck I'd get, but going up?), but I'm not about to tell it to stop! *grin* And I can turn the graphics settings up all the way in a startling number of my games, at native res. (I am actually surprised that it looks like I will not have to replace my graphics card this year. Yay!)
I hear that an 8800 GTX is that much faster (about 40%ish?) that the CPU is the bottleneck on many current games until you get to 1920×1200. That makes sense to me; what the effect with future games will be, no-one can really say for sure of course.
But I'd definitely say 24" over 22", for basically the same reasons Elric said.
The reason I had my heart set on a decent 24" was that 1920×1200 means 1080p, the top crown king of the HD resolution we'll probably be seeing more and more over the next few years, actually fits in the native res. To me, that gives the screen a certain amount of future-proofing that felt, and feels, "worth it" (i.e., worth the cash premium) over compromising on a lower res.
And as Elric said, you keep monitors for longer than graphics cards. In fact, I'd say graphics cards may be more or less the "shortest-lived" of the computer components, which is to say they seem to be getting better, far quicker than everything else. Good monitors, on the other hand you feel tempted to keep until they wear out or look awful — and much as I'm iffy on predicting the future where this stuff is concerned, I doubt that 1920×1200 will look "awful" at any time in the next few years.
Of course, I could be wrong; half the fun in building computers is trying to speculate on the future and figure out when and where the "sweet spots" seem to be, and they're not always going to be in the same place for different people with different budgets and desires — but, well, there's my opinion added to the mix.
Whatever you choose, good luck with your build!
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