I would suggest that perhaps nitro *can* allow you to tune an engine to run cooler (by richening it up a whole lot (beyond the ideal stoichometric ratio) and thereby sacrificing some of that extra power for lower running temperature), BUT, if you tune for max RPMs then your engine *will* run hotter. Here's some supporting evidence.
If you were to run 100% nitro as in a dragster then the richer you run it the more power it will make, this is true till the spark cannot ignite the mixture. One of the major increases in HP in these engines is the development of huge electronic magnetoes which allow the mixture to be run richer. If you watch the competitions you will see raw wet fuel come out of a missfireing cylinder at the starting line. Looks almost like water running in spurts from a garden hose. When you run 25% or greater nitro then it will run cooler at peak power, but it will get much hotter than low nitro if you have a lean run.