Don't trust Asus Probe, it's ****e (ie. it lies).
The BIOS reading is correct - as is the reading you will get with MBM5. For some insane reason, Asus Probe gives the temp on my A7V333 about 5C higher than it should be.
Some hardware website (can't remember which one sorry) I read did a test with thier own thermal probe and found that the BIOS on the A7V333 was giving the more accurate reading. I don't know if this is the same on your board, but it's still Asus so the same may well apply.