So wait? If i run it warmer will that wear my engine out more but give me more fuel efficiency? And if i run a little colder it won't wear as much but my MPG will suffer?
So this is again very generalized so don't think this is 100% true on all engines in all cases, but as a rule of thumb, your engine is most efficient mpg wise in that 210-215 range and suffers less wear at that temperature. Anything outside of that affects mpg and wear on your engine. This is why on modern fuel injection vehicles, it's actually better to drive them as soon as you start them so they come up to temperature quicker and thus suffer less wear. Your bearings suffer the most wear when the engine is cold, and when cranking your engine.
Running the entire engine colder means that while you are potentially warding off k/r and detonation, you are increasing the wear on your engine and you mpgs will suffer. How much? Probably not a ton, which is why a lot of guys running high boost tend to opt for colder thermostats. What I'm saying is that without supporting mods to your car is that the base temperature will be the same roughly even with a colder thermostat, the only thing a colder thermostat will do is potentially keep your engine colder initially which is great for short runs on the track, but doesn't do much for daily drives since your temperature will come up to around the same temp anyhow.
If you're talking running colder all the time, that requires supporting cooling mods such as changing your fan times, upgrading your fans, thicker radiator, porting cooling passages, and such. All of those things with a colder thermostat will keep your engine colder all the time which would help decrease k/r.
All I'm saying is that there are other mods that help reduce k/r which while may not be as cheap initially, do a lot better job of reducing k/r, and don't affect engine wear. Just choose wisely!