Mike, I don't have anything close to a thorough temperature profile for Penns Creek. Maybe some Penns Creek "regulars" can provide better info. I think putting temperature monitors in Penns Creek and its tribs would be a good fisheries research project.
Also, it's hard to define thermal categories, since it's an incremental thing. In a drought period one section might reach 81F, another 79F, another 77F, another 75F, another 73F etc.
Where is the "line" between what is a "warm" or "normal" section?
But here's a rough summary. It comes out of the cave cold. From the cave down to Spring Mills is mostly posted, so I haven't fished much there. There is a substantial spring at Spring Mills.
It gets what I consider a pretty warm stream somewhere between Spring Mills and Coburn. I don't think there is a "line" but IMHO, where it's gets pretty warmish is closer to Spring Mills than Coburn.
The influx of Pine/Elk provides substantial thermal refuge. But in hot dry periods, if you go down a little ways from Coburn, where the waters have mixed, it still gets quite warm in droughts. Pine/Elk at its mouth is not ice cold during summer droughts. It goes into the low 70s.
The freestone tributaries further down provide thermal refuge. There has been a lot of discussion on here about closing or not closing the areas where trout stack up during droughts.
In summer drought periods, bass are commonly caught near the PFBC cottage in the C&R area. I have seen them above Poe Paddy, at the railroad bridge at the tunnel. Friends have reported seeing them near Coburn during droughts.
Riparian forested buffers on Penns Creek and its tributaries would help a lot. Some sections are buffered now. But many are not.