Google a program called Game Booster, all us Mount and Blade players use it to prevent our mods from crashing in game. It good because when you activate it with a game or just simply turning it on on your comp it makes all unneccesary programs that are running stop running, so if any of those programs are whats causing the lag, and you dont want to painfully find and close or find and uninstall useless or default programs you dont want, this allows you to do that. Sorry to sound like an advertiser but it worked nicely for me.