I wouldn't go higher than 1.5V under air.
So you would put 1.5V under water or phase? The only difference between air and anything else is the temps, so you need to judge it by that, not by the volts.
Would the chip last tho at this voltage for normal (non-benching) use?over at XS a guy ran 1.92v through his Q6600 under LN2 and was benching @ 5.134ghz