I edited the preferences.txt and changed the unit size to 100 (so larger than large but less huge than huge). This gives a good balance in my opinion. Oh, I have a Radeon 9800 Pro which does OK up to about 5000 troops. On a slight tangent, I believe the amount RAM your PC has is actually more of a contribution to the speed of this game than just the graphics card. When I went from 512 to 1024mb RAM, it certainly improved my frame rate.