Update: Ever the experimenter, I went ahead and brewed it anyway. I did a split batch with 5 gallons fermented in my chamber at a controlled 64F, and 5 gallons in the FermZilla at room temperature (a constant 70F in our house) and 8psi +/- via the spunding valve. I used Wyeast 1318 London Ale III in both.
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The traditional beer took nearly a week longer to reach FG and has berry esters that I find to be a little distracting. I haven't kegged and carbonated that one yet, so these are just carboy samples at the moment. Still tastes good, though. I'm crashing that one right now and am due to keg it later today, so if it's remarkably different/better after that, I'll update below.
The pressure-fermented-at-room-temperature beer is excellent. No fusels, limited but still present berry esters in the background--the levels compliment the beer beautifully rather than overwhelm it for me. Day_trippr, you're correct above in that pressure mutes those esters, but it seems like there might be a sweet spot depending on style, preference, and yeast related to pressure/gravity/etc. The beer also had a nice roastiness without being over the top. The beer is anything but muted or dull--it's surprisingly much better than any other porter or stout that I've brewed in the past.
Currently I've got a weird hybrid beer fermenting at 6 psi in the FermZilla--it's a Pilsner malt grist with just about 3 ozs of Acidulated malt, Magnum for bittering and an ounce of Mittelfruh at 10 minutes. The yeasts used are 50% 1007 German ale and 50% 3787 Trappist High Gravity. Sort of a Kolsch meets Single. I wanted to see if fermenting under pressure would strip the beer of its 3787 yeast character and make it more clean like 1007, or if it would have some elements of 3787 in it.
I guess my big curiosity is whether or not there's a generally applicable sweet spot/balance in pressure fermenting between OG, temperature, and pressure that allows the yeast to express itself well without bringing through the high temperature-caused undesirables. For example, if harsh fusels can't be produced in any beer at room temperature and pressure above 10psi, but esters still show up, that might allow one to brew high gravity beers using yeasts that traditionally throw fusels at high temperatures. My first Scotch Ale was about 8% ABV and tasted like rocket fuel after fermenting it at 70F ambient in a closet (who knows what the internal beer temp was). Wonder if that beer fermented under pressure would've turned out.