The T51P was the most comfortable on ear I've tried...in the Sennhesier/Beyer style. I've given up on On-Ears; I love the isolation but they're always painful after about 15 minutes. I think I've figured out which part of my ear hurts; or maybe its the ear/glasses combo...I'm not sure. But the T51P was def the best of the DT1350, Amperior, HD25 lot. Fwiw, I found the M500 more comfortable.
Haven't tried T51P, but the T50p is really uncomfortable for me.