I've seen discussion on this on a different subject and some people say that the slight restriction that the thermostat provides aids with keeping the coolant pressure up/slowing the flow down so that it can asorb more heat. Wherther or not that is true is debateable, but it does seem logical. There is also a school of thought that say you might not be able to get the coolant up to temperature as it is over cooled on startup.
As far as I can see, the only thing that the stat does is let the engine warm up quicker - if you want the car to run cooler then you are probably better off sorting some ducting to/from the rad to maximise pressure differential over the core?
