Temperature vs. growth rate is always a healthy debate. I've heard and repeated - that if you're cozy in the room, so will be your cubes.
PE is generally recommended as a potent strain - I've no experience with that one, but it's a commonly repeated subjective experience. I'd say that PR is a more potent strain than, say, GT.
Again, subjective experience, somewhat backed by repeated subjective experience that most peeps can agree upon to some measure.
That said, if you grow your PEs at 68 degrees - to suggest they're 25% more potent -
I'm not doubting that you grow some potent stuff ... hell, I've been in love with a variety of strains. Serious Man=Fungus Love I'm talking here.
But the potency wasn't me. It was the mushroom. Or maybe the substrate. Or maybe the meteor shower, or the conditioner I used to eradicate the smell of decaying flesh from my body, right?
To suggest that I'd dropped the temperature in the room eight degrees, thereby making them 25% more potent would . . .
belittle the organism that really did the work. Sure, I provided the habitat and the proper nutrients, but if I could alter the organism that much with an eight degree temperature shift?
I'm gonna go open all the windows in the house. If I don't wake up 25% more potent, my GF will have words.