I still need to insulate the vat, which might decrease the time a little (though I'm not sure it will do much--most of the time the milk is below room temperature and insulating will actually prevent heat from entering the milk from the surrounding air). I'll be working on that tonight and will try to report on what affect, if any, it has when I make cheese again this Friday. The best way to speed up the heating, with my design, would be to add another heating pad. The problem, then, is how many amps can your circuit take? I'm pretty close to the limit on mine with 1180 W.
Unless you are making really big sous vide meal, this might be overkill. The 4 gallons isn't very deep in this sink and, from what I understand, sous vide should have the food pretty well submerged.