The pressure in tires is controlled by the combined gas law:
https://en.wikipedia.org/wiki/Combined_gas_law
The pressure will be proportional to the temperature in degrees Kelvin (same as degrees Celsius but starting at absolute zero). This assumes the tire volume does not change with changing conditions or temperatures, which I think is roughly true. There should be no difference between the case of 100% Nitrogen or 80/20 Nitrogen/Oxygen. Any small amount of water vapor will have no effect as long as it does not condense out. There is a lot of snake-oil hype about Nitrogen out there lately, if you ask me.
I agree that there are problems going too high. Handling can get bad. You will feel silly if your car ends up in the ditch, because any small savings you previously made by running high pressures will be consumed fixing the car. Also the ride just gets harsh. If it is harsh on your ass, it is harsh on the car components too.