Use HWInfo. By far the most powerful and versatile system monitor and I've had the best luck with it being accurate compared to others. Temp readings on AMD chips has always been kinda weird. They have two CPU readings, one is the CPU's actual physical temperature, usually measured on the socket and is usually called CPU Tctl. The other is basically a fake calculated temperature that doesn't fluctuate as much and is less "accurate", usually just called CPU temperature. Depending on the software they might interpret these differently. AMD does this to smooth out cooling performance so that the constant flux of Tctl doesn't change your fans constantly.
I'd cross reference them with RyzenMaster as the temp it reports is the faked one. It's what is used to control fans by default and also what you would compare to the max temp for the chip. Figure out which is which and use the faked temp. I don't use RyzenMaster at all, but it's a good way to know which temp is which.
I personally don't like running my 1700 above 70oC but I'd say anything under 75-80oC during stress testing is fine. They'll throttle or shut off completely at 95oC. Mine usually is in the lower 60's for CPU focused gaming but will creep into the low 70's during stress testing.
Depending on your motherboard you might be able to control which temperature sensor the board uses to control the fans, my Asrock does.
Edit:
@jamesd1981 I'm pretty familiar with the Ryzen platform as I did a lot of overclocking and tweaking when they dropped the first gen of them and before AMD worked out a lot of the bugs. If you have any questions let me know.
@beers has a 2700X as well.