Regarding the comfort issue, today I spent 4 hours playing WiiU non-stop, and I had no trouble. Actually when I turned off the console, I took my headphones and plug them to my smartphone to listen to some music. That was about one hour ago and so far I have never taken the headphones off. That's about 5 hours using the Momentum non-stop, without feeling any discomfort.
Now that I mention playing WiiU, I loved the experience. Since the WiiU GamePad has a regular 3.5 mm headphone jack, I could plug my headphones directly without the need for an adapter nor a dedicated headphone (I know Sennheiser produces some dedicated cans for gaming). The results were quite surprising: I could track where sounds come from. If something was happening to my left, I would hear it on my left ear, and so on. It felt almost like if it was a an open back phone. Now I know why some reviewers say the Momentum have one of the best soundstages for an open can (something I didn't actually believe until now).
If this is how a closed headphone sounds, I can't wait to put my hands on an open set. Probably when I can afford it, I will get a pair of HD598, HD600, or 650 (I have some non-Sennheiser candidates, but I think that's for a different thread).