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