100-120C is high, 120C is very hot, 100C is hot but not a dangeours temperature, 70C is perfectly normal and 60C is a good temperature, lower than that and they are chilly temperatures.
Rule of thumb is, if your card artifacts, its not good enough to run at those clocks, if you set certain clocks and your card runs perfectly at those speeds you have nothing to worry about, if your card runs for 6 hours straight under load with no hiccups, its perfect, as I say OC limit is determined by card stability and not temperature.
I hate when people claim their card is overheating when it gets to 70C under load.