Depends on your cooler.
Some people say max 24/7 is 1.38v. Others claim 1.425v is fine.
As you can tell, I'm with the second group.
Regular CPU temps guidelines - don't go over 80C for 24/7.
You should be fine with any high-end air cooler.
Just make sure to run Prime95/ORTHOS for at least a day if you end to do Bigadv for 50,000 PPD.