It's got a mild overclock to 2600. Any further than that and I'd have to relax my memory timings a tad, which I don't like to do.
1920x1200 monitor. Currently have an X1950Pro.
2.6Ghz and that resolution sounds quite promising. Although the GTX is suited for higher resolution gaming with the X2 3870 being the best. I think the GTX and X2 3870 will be better for 1920x1200 although I'm a bit cloudy on the GTS's performance at this resolution. The GT wouldn't be advised for that resolution.