24/7 or suicide benching?
Benching you could probs push it up to 2V, ive seen it done, but anything over 1.85 tends not to help v.much
24/7 i would stick to 1.8ish, you can usually get the max stable out of your chip pretty much with that, anything more tends to only gain you a few benchable MHz (though this is not only the case, just a generalisation).
In the end you've got to balance how much you need the extra speed the voltage will get you, and how long you would like the chip to last.
G
