Thats enough, when going to campaign map it just is buggy. For most of players.
If it lags when playing with medium settings, you must tweak you computer somehow. Firstly shut down all uncesessary programs, Gamebooster 3 is good for this!
Seriouselly, Warband uses very old engine, so if it lags (for other reasons but conflicts in mod) get a new computer. (but first try tweak old one)