I've said it before and I'll reiterate it now: A lower temp thermostat will not fix any cooling problem, other than one caused by the thermostat itself. If an engine/cooling system typically reaches a peak of 210, 230, whatever, it will still do so eventually no matter what thermostat you have in there. A thermostat merely restricts cooling in the first few minutes of operation and in extremely cold weather.
If your engine is truly overheating (and by that, i don't mean the gauge is reading hot, that means nothing), you probably have a clogged or bad radiator, a bad water pump, or some kind of restriction. It could even be air bubbles trapped in the hoses. Unless the thermostat is stuck closed, which is very rare, that would have no effect on operating temperature. You could remove the thermostat entirely (basically, a zero degree thermostat) and it would still eventually overheat if you have a problem.
Forget about thermostats, and address the real cooling problem, if there even is one. If you suspect it, take a temp reading at your upper radiator hose, and go from there.