I think temperature is much less critical with model aviation. You do need adequate cooling, and temperature is probably more important in CL stunt than in RC flying (because we don't have throttles -- we depend on the engine's self-regulation, which gets messed up if it gets too hot).
But it is by no means the be-all, end-all detail that you're concerned with. Proper props and fuel, getting the right sort of engine for the right sort of run, getting your muffler or pipe set up correctly, getting your tank right, etc., all matter a great deal more. Even when temperature is mentioned, it is in the context of "if your engine is acting like that then it's too hot.", not "what does your IR thermometer read?"