The key thing that happens with a higher temperature thermostat is kinda a surprise.
With hotter coolant behind the cylinder wall, the oil on the wall thins out, the viscosity goes down, and there is less friction against the rings.
Running a hotter thermostat is not much different than running lower viscosity oil, except that your main and rod bearings still get cooler higher viscosity oil.
Not all parts of an engine need the same lubrication.
At part throttle (not full throttle) the hotter coolant will heat the intake air. This is normally undesirable at full throttle when you want maximum horsepower, but in the case of 'daily driving' part throttle the heated intake air makes you use more throttle opening which raises MAP and the higher MAP helps push the piston downward on the intake stroke and allows the engine's other cylinders to not have to supply horsepower to draw that cylinder downward against a vacuum.
Complicated, ain't it?
In this way heated intake air is like exhaust gas recirculation (EGR) .....but heated intake air has two disadvantages compared to EGR:
* it makes detonation and pinging more likely and can limit part throttle compression ratio limit
*it takes slightly more horsepower from the other cylinders to compress the hotter mixture on the upstroke of the piston
Notice the newest diesels have gone to 'cooled' EGR? It is better for MPG than either heated intake air or hot EGR.....but it loads the lube oil up with soot