Slightly oddly (until you think about how much of it there is on a battlefield) setting grass/vegetation detail to lowest setting may have the biggest positive effect on battle map performance. When I went up to 'large' unit size, I had to tune most visuals down or off to get a good game, especially when battles were between 2 at- or near-full strength armies. The strategy map commands for cities & unit moves on the strategy map were always fine. Similar to Hussarknight, I started playing the game on a 2.6 gHz P4 with 512 mB SDRAM & an nVidia 5200Fx with 128 mB memory. IIRC, most of us felt by the time that RTW had been out a few months that you really needed about a 2 gHz CPU for a fairly satisfactory game experience. There is pretty much nothing you can do about this. The larger the yellow 'circle', the worse the lag. This is because, I expect, the game repeatedly calculates all possible paths your army can take in order to create that yellow area on the game map to show you where it can move in one turn. I think your biggest problem is the CPU itself. On the campaign map, when you click on an army youre gonna get a noticable decrease in FPS.
