I recommend for all people who still have this issue to reapply thermal paste cause the factory application is sometimes really bad they put to much as need and that cause higher temp. Before I get 90C on GPU and 105C on CPU at full load and 37C and 45C at idle. But After a light tear down and cleaning the heat sink and new thermal paste application, I get 80C max on the GPU and much 95C on CPU at full load and 27 and 35C at idle so yes that's an improve of 10C, I use Arctic MX-4. But I can also say that CPU are design to go up to 105C and I still get this temp sometimes in full load so that's not a problem cause he throttle itself when he reach this temp and the fan goes up anyway even if for me it take much time than many macs I got to. Apple probably choose to don't up the fan before a high temperature because it's design for same if we know it's much because they want focus on silent. You can use an app like Temp Gauge Pro who's for me the best for thermal regulation and monitoring with the Auto boost...
