I also trust the BIOS temp as well. I was trying to compare those temps with the in OS temps but I couldn't do consistent results. I'm using the stock cooler.
Also mistake in OP: HWiNFO64 temps had a -12°C modifier (was doing some testing, a friend told me that -20 is the actual temp). So actually that would be 54-56°C idling. But even that feels wrong because stress testing the CPU makes HWiNFO64 read 82°C! Surely that can't be real, given AMD states the max temp should be 72°C.
I tried making the CPU temp in HWiNFO64 go as high as it can (84°C), then quickly went into bios and checked the temp - 40°C. But surely the CPU would have cooled itself before I got into the bios.
Any ideas how to set HWiNFO64 to read accurite temps? Or how to do tests?