That's RTW mate, or what I like to call the "3D world". It is simply, like.. almost impossible to run a 8000 men battle with all graphics on max with a good FPS rate (30+) in RTW.. I didn't test any new cards, but I know that 8000 men on the battlefield with GFX set to high and on M2: TW is like a miracle to happen with the normal PC home-users..

P.S. A Cavalry unit count to 27 men in RTW. An "elite" infantry unit count either 12 men or 18 men. A normal one counts 41/40. A stacked one count 60, and the odd peasant unit counts as 80.