EarthQuake, "Delete History" i've already bind to HotKey, well as "Delete UV". I always try clear (Scene/High-Poly Geo) before 'bake/export/render'. "Sub-D History", if you mean "Construction History"... I've clear this all time.
Make sure to delete history before doing any bakes in maya, save a backup of your scene as this will drop your sub-d history etc. This should speed up bakes significantly.