Solution
I'm home now, and can see it.
HEC released a lot of junk a few years ago, but if this one is indeed 80+, it was run at 100% of its label for over half an hour during testing. The temperature was an unrealistic 23C, but it didn't die, and it handled the load efficiently, so it probably wasn't close to dying either. It should have no trouble with a HD6770.
I'm home now, and can see it.
HEC released a lot of junk a few years ago, but if this one is indeed 80+, it was run at 100% of its label for over half an hour during testing. The temperature was an unrealistic 23C, but it didn't die, and it handled the load efficiently, so it probably wasn't close to dying either. It should have no trouble with a HD6770.
 
Solution