Warband's max setting is 150 soldiers. For the first Mount and Blade game, there was a mod that allowed you to change the total number of soldiers to 1000, though I could only run it smoothly at 400 soldiers.
As I bolded, I know that. However, I'd really like it to be able to support high numbers and have the game still run well. Obvioulsy hardware plays a role in that, but I think the battles are so much cooler with so many soldiers (except for the seige battles of course).
Granted, I'd rather play with cheats and and give myself unlimited money and health just to take part in the largest battles possible.