The Sig DJ is a leap forward in comfort over the M-100. The cups are spacious and deep with plenty of room for my ears to fully fit inside without touching anything. The earpads and headband use the softest leather I have felt anywhere. The clamp is a bit on the snug side which has never been an issue for me, but some have commented about slight discomfort after a few hours. I have actually fallen asleep with them on and not had problems. You may want to check out the
Sig DJ thread for more feedback, but they are a fantastic headphone.
When I go back to the M-100 after wearing the Sig DJ, I immediately notice how small and thin the M-100 pads feel by comparison.
While the Sig DJ does isolate well, I don't know that you could fully appreciate their sonic benefits over the M-100 on an airplane.