AMD Dual core @2.6GHz (each); WinNT (OEM Vista 32 bit); ATI Radeon X1650 SE; 2 GB RAM.

Maxed everything out, at a resolution of 1900x1200. Only a slight bit of lag -- usually full stack vs. full stack; or in (larger) cities.

M2TW battles with everything maxed out have a noticeable amount of lag though, even in smaller battles.