I checked all 4, but they all read the same temperature. Somehow Tthrottle was reading the same sensor from GPU-Z 4 times.
It didn't see HWInfo at all. And I don't like this: "HWiNFO, when using the installer, the 64 bit version stops working after 12 hours."
I've taken the easy way out, I just lowered the clock speed for the offending GPU.