BigBen:
You should not be disapointed.
I currently have (2) XMS PC3500 256MB running 210FSB w/ CAS 2-3-2-2 settings. I am even stress testing them at 215FSB w/ CAS 2-3-2-2 settings right now with great luck.
The resaons why I went with the 256MB vs 512MB is two fold.
1) The larger memroy sticks require more current (not necessarily voltage) in order to run them properly. Since I am already pulling a very large load on my 5V line, I didnt want to tempt fate.
2) Sometimes larger sticks dont tend to allways hit the highest FSB settings or RAM timmings. However there have been several people who have done just fine, so this point is negotiable.
Enjoy!!