One thing I've noticed is that it (base M4) seems really reluctant to push the fan speed up. I play around with some distributed computing projects and I currently have it doing some PrimeGrid work. CPU temp quickly hit 100 °C but the fan speed stayed at 1000 RPM. Guess Apple figures that's okay? It concerned me a bit, though, so I'm running Fan Control now to keep it in the 80s. The case stays quite cool even when the CPU temp is high. It seems like it would be better to pipe some heat to the case, though I suppose Apple engineers know better than I do.