I'm not exactly sure why, but for me the emx500 shells are uncomfortable to sleep with, whereas I can (and do) sleep with the graphenes. I think they shell sizes are comparable, but the graphene stems are a bit thinner, which might be what makes the difference for me.
Btw, thank goodness my better half is trained to accept buds stuffed into my ears when I go to sleep, because I don't think I could sleep very well without them. When nothing is playing, they block out a bit of sound which I find helpful. But when higher volume sound wakes me up and really annoys me (damned cat for example, or better half getting up early to go to work), I just press the power button on my X3 and a few seconds later the trance goodness is soothing me to sleep again
Edit: I'll have to try the monk lites for sleeping with - they might have the perfect size shell/stems.