[breweite]

I made an 8% beer from a new 3711 starter. It got a little on the hot side and threw out heavy phenols. Still very good beer, just not my personal preference. I personally like to ferment 3711 in low 60s, and I'd like to do it again with this same yeast I just harvested. Would this have any impact on the new beer if I try to ferment low? Has the yeast mutated a bit? I don't understand the chemistry going on so any insight would be helpful.

I have reused many 3711 yeast cakes with no ill effects, however, this is the first time one got a little warm on me.

[majorvices]

I wouldn't worry about the temp of fermentation for harvesting. The temp was probably perfectly fine for the yeast, even if it didn't make the best flavors. But general rule is that most brewers don't pitch from a beer whose SG was too much above 1.065. Personally I feel that this number is a bit conservative, but an 8% beer may be pushing it. Yeast tends to have some mutations when the ABV gets too high and the resulting flavors might not be exactly what you were expecting.

[brewinhard]

+1.  I too would be more concerned about the alcohol content instead of the hot ferment temps.  Just for some background on this one I once brewed a 7% saison (WY 3724) and was using a brew belt without a temp controller (way back in the day).  The beer got upwards of 95-100F and I thought I killed the yeast only to find out it fermented the beer perfectly. 
I then repitched it into an 8.5% dark saison and the beer took right off and also fermented quite well (dried out to 1.010). 
So repitching from a hot ferment is just fine (at least with saison yeast) IME. 

[Steve Ruch]

I wouldn't worry about the temp of fermentation for harvesting. The temp was probably perfectly fine for the yeast, even if it didn't make the best flavors.

Yeast will happily reproduce in temperatures that are too high to make good beer: two different things.

[reverseapachemaster]

I take 3711 up to 85-90F without problems repitching.

[majorvices]

I take 3711 up to 85-90F without problems repitching.

Missed that it was a saison strain. Even better!

[HoosierBrew]

I take 3711 up to 85-90F without problems repitching.

Same here.