Long Story Short:
Maximum 65ºC during gaming, I'd say its All Good!
RX6600 is a much better card than the RX570, the Polaris cards were very good but its showing its age.
Although, the RX6600 may not be as future proof today as the RX570 was, with that said:
If you are on a thigh budget and can spend a few bucks more, get the 6650XT. You can squeeze an extra 10fps and sometimes more.
The Englishman