A 165 opens sooner than a 180 degree thermostat. None of this alters the top running temperature.
Only true if you've put more heat load into the radiator than it can handle. As long as the cooling system is adequately sized, the thermostat will regulate to very close to the thermostat temp. In other words, a 165F stat will keep the engine at 165F max, and a 180F stat will keep it at 180F max. If your cooling system is on the ragged edge, the cooler thermostat would be full open just like the 180F stat, and the engine temp would be fully dependent on the radiator and cooling system capacity.
