I can only go from my XP2000 ( 1.67gz ) to an XP2400 ( 2.0gz )given
my current MB ( which I am not considered changing at this time ).
I am running W98, FX5900 w/det45.23, 512MB Ram.
Not sure if that small step in CPU upgrade will make a lick of difference. Are Mesh and AI-traffic CPU bound - as those are the areas that I tend to experiment/adjust downward to gain FPS.
Running 1600x1200, 2xAA, 8xAF, Clouds 100/max, autogen ( normal or dense - can't decide ), vis=60/cloud draw=60. Getting 12 - 18 on complex approaches.