I live in San Antonio, where it only varies from summer hot to winter cool. It is never cold. I've run both 180 and 195 high flow thermostats, and in summer heat there is very little difference in max temps. The max temp is determined by the radiator/fan setup, not the thermostat.
I have a stock shroud and thermostatic fan clutch, and in extremely hot weather (100-110 degrees) while idling it may hit 215-220. However, this is within the normal range with a 16 lb radiator cap. In winter weather it will never go above about 195, which is the rating on the thermostat.