Good question... software monitoring and the SMB's voltmeters are often not entirely accurate. The only real way to be sure is to put a voltmeter on the CPU pins.
I'm on an 1800+ like you and MBPROBE says 1.82 volts, AIDA says 1.66, my voltmeter fluctuates between 1.73 and 1.68 with load...
I tend to believe the voltmeter.
--->It ain't better if it don't work<---