Originally Posted by Just a nickname
Degradation will occur faster with high temperature. If I was you I wouldn't risk this. Wait for DICE or LN2. I don't think you need ln2 though it is safer if you are planning using high voltage.
DICE will brings you to minus 70-60 while LN2 170/160.
Degradation happens continuously, the transistors will need more current and will run hotter. A circuit could degrade and cause general instability. Voltage is part of the problem since it increase the temperature. Even if you are on "safe" range of temperature, the combination's of frequency & temperature != safe.
90C 24/7 stock speed could be equivalent with 24/7 70C at 5GHz in term of "safety" (just taking that from my hat, but you see the point, it is important keeping temperature low on high voltage, even if you are in the "safe" zone).
Edit: To all of the comment concerning voltage usage, running on lower frequency with high voltage won't degrade as much as if you were running faster with the same voltage. Each cycle (5 000 000 000 in one second at 5GHz) the transistors change of state thus releasing current & heat and degrading a little in the process.
So yea, 4GHz vs 5GHz is 1 000 000 000 more cycles per seconds.
Safe voltage does vary dependently the temperature you are running at.