i gotta say although ur right about variables, the heat needed to heat cycle and engine will always be the same as most high performance engines are abc or aac so to heat cucle them you will need so much heat which means a temp will be needed.
im 17 so i could be wrong but i understand when u heat treat metal as long as its the same metal (like most engines are) then the same heat is needed.
i come from junior drag racing where we have the option of exhaust temps and let me tell u head (at the glow plug) arnt visible enough to be a tuning gauge an exhaust temp will tell u the richness or leaness of an engine so i think every one is temping the wrong end but u cant really temp and exhaust in an rc car so thats life.
ull be interested that head temps are similar with my drag car (bout 250's farenheight at idle) and thats 750's f at exhaust and a change of 60's can loose .11 of a second over 1/8th mile. so u see why exhaust would be better? and it can be done (30 gram sensor)
most 'americans' say u need 200's farenhight before u turn the engine over other wise the friction can ruin the piston and sleve so i think that makes more sense than worrying about 10's celcius running temp.
im saying this from my understanding of metal and heat transfer and also racing back ground i have only ever owned one nitro cr and i wore the engine out in 2 litres (air cleaner came off).