But what I wanted to know is what are the safe temps for the liquid
Below 100C, since more from that point, it may vaporize. Then again, not all liquids in AIOs are pure distilled water, instead, some use additives in the liquid, rising the boiling point.
The thing with liquid temp is, you have no idea where the temp probe is located. Is it in the pump intake? Pump outlet? Rad intake? Rad outlet? Since it plays a role on liquid temps, depending where temp sensor is.
All-in-all, AIOs are designed to cool CPUs (or GPUs) that can reach 100C. So, it would be bad idea to use a liquid which "safe temperature" is only ~50C. 60+C and then what? It boils/vaporizes?