Fact: with the engine oil cooler in place, operating as normal, the average mean engine oil temperature will be within a few degrees of what the coolant temperature is. At very high friction surfaces like the cam lobes, the engine oil temperature will be much hotter than the average oil temperature.
Thin oil flows better, has less pumping losses.
Unless you have tuned the computer to make use of the 180 degree thermostat, I would recommend sticking to the factory thermostat.
A hot engine is an efficient engine, the lubricant has thinned to it's intended viscosity at operating temperature.
I don't understand the reasoning behind the use and recommendation of a 'thick' oil. Automatic transmissions create a lot of heat, and they use very thin oils, compared to an engine. Does anyone use a 'thick' oil in their automatic transmission?
Would an automatic transmission benefit from using an oil as thick as 85w140 gear oil?
If it did, you would bet your bottom dollar that manufacturers would start using them.