I loved the sound of the M-100s, but the combination of the clamp, shallowness of the ear pads, bass, and the smell (they really smelled of spray paint) gave me a headache after more than an hour of listening. The Sony and PSB seem to be considered more comfortable than the M-100s, at least for people with larger heads and larger than average ears. I'm going to try to head to a Sony store to try out the MDR-1Rs to see how they feel before I buy, since I didn't have a chance to do that with the M-100s.
Had both the MDR-1Rs and M-100s, the Sony's are DEFINITELY more comfortable by a mile (it has been one of the most comfortable headphones I've tried these past few years). BUT, I found the mids to be very accentuated and especially, there seems to be a region in the upper mids that causes a bit of fatigue TO ME. It seems others are Ok with the overall sound and some others mention that these are better at lower volumes... (probably due to the mids/fatigue factor...).
Its just interesting how often the comfort aspect is brought up... interesting insofar as I expected problems, originally intended to wait for the XL pads, skipped that due to the unclear timing and was positively surprised by the status quo: I don't have any problems for my usage pattern and find them quite comfortable and definitely my most comfortable mobile set.
Furthermore I let several people try them out and in most cases the second thing they mentioned after the sound was that they found them to be comfortable (none of them found them so uncomfortable that they felt the need to mention that and they all did not just try them on but listened for some time). Yes, of course there are more comfortable headphones available, but most of them aim at completely different usage scenarios (i.e. home / studio use only).
I didn't have any problems with them in half-hour increments... If you give them for people to try, they might NOT notice any comfort issues if they only have them on for 10 minutes or less... Try most of the day (at work I AT LEAST use headphones for 6 hours of the day... maybe more... #CubicleCodeMonkey ) and it's very apparent and your ears feel the pain. That's basically THE ONLY reason I sold them. The fact that also one of the wingtips was cracking turned me off. When I get them again, I will definitely NOT pay full retail for both headphones and XL pads... :-p