Pea Ridge is a goon 'un. You can do Elkhorn tavern and Leetown on the first day, and the whole giddyup the second day. You can even do a mini campaign, where the fights on the first day affect the battle on the second...
Mill Springs could be a good one too. Smallish, with either side of 5000 per side - you just use battalions/regiments instead of brigades, but I think BBB could do it...