A lower temperature thermostat my extend the time it takes to reach a steady state temperature while idling or in low speed traffic because it will sent full flow to the radiator sooner, but the steady state temperature in traffic is ultimately determined by air flow through the radiator.

Say at 90F ambient it will take longer to get to 105C if you start out at 80C rather than 90C, but in extended bumper to bumper traffic both will eventually achieve the same temperature range, which is controlled by the fan algorithm.

Of course, in steady speed driving, especially in cooler weather a lower temperarture thermostat will reduce operating temperature because there is enough radiator heat transfer capacity to keep the temperature just above themostat opening temperature.

Aluminum engines like to run hot - either aluminum head(s) or all aluminum engines. Since aluminum only has about one third the thermal resistance of iron, they more readily transfer heat to the cooling jacket - heat that could otherwise be turned into useful work at the crankshaft. The hotter an aluminum engine (within reasonable limits), the better its thermal efficiency. Also, higher coolant temps tend to reduce engine out emissions and reduce blowby condensation in the crankcase.

I recall about 20 years ago I was running my Cosworth Vega with the Porsche Owners' Club at Riverside. It was about 105 ambient, and the CV was running hot because the radiator was getting clogged up with silicates and other salts from the traditional green antifreeze. The coolant temperature stabilized at about 230F, and gave me some concern, but it had never run better. Not long after I removed the radiator for a "rod out" and operating temperature dropped back to the normal 195F.

Duke