CPUs and GPUs temperature ranges
The manufacturer's reccomendation is always definitive. Outside it, you may have problems; inside it you ought to be fine.

I believe that modern systems (AMD and Intel) will self-throttle in order to maintain safe temperatures. This isn't entirely reliable if your cooling system is inadequate, but it will stop it from self-destructing. Temperatures above 125C are definitely harmful for normal ICs.

(I have a laptop which will report temperatures up to 90C before going into emergency shutdown. The thermal throttling doesn't quite manage to keep it in acceptable ranges.)