OK, I'm pulling rank for just a second. If you understand what a Mollier diagram is, you are excused.
A higher pressure cap allows the temperature of the water in the engine to go higher, along with the
pressure of the water in the engine going higher, before opening and releasing pressure. That release
of pressure will allow the temperature/pressure to remain the same, higher T and P, until you run out
of water/steam.
A higher pressure cap keeps the blow off of excess pressure at a higher pressure and temperature.
I'm sure, though I don't have a curve at those pressure/temperatures handy, that the temperature
is still perfectly fine in a modern MXer. It may be only a fraction of a degree, based on this curve
I have here with far too little resolution in the range of interest.
Water wetter and similar stuff has a different enthalpy curve though I've never seen one published
and don't want to look today. Antifreeze mix I know has a higher boiling point than pure water, allowing
that pressure/temperature curve to move down in enthalpy so that at a given pressure, the temperature
is lower. I bet the water wetter stuff does the same but hope they have a mechanical engineer on
staff.
You're welcome and no, unless you have a license to practice engineering in the state of Ohio,
I'm not interested in arguing with you about it.