It's meant to be very large. My head is of average size I feel (around 23inches circumference above the ears) and the AD700 fits very loosely. I'd describe them as being ill-fitting, but extremely comfortable. You get use to the loose, wonky fit after a while, and they become extremely comfortable.
I personally found the AD700 to have a bit of front/rear positioning trouble compared to something like the DT990. Compared to higher end cans, the AD700 also sound rather off-timbre overall as well, but their soundstage remains ridiculously large and spacious even with DH. I can't comment on the PC 360.
Edited by TMRaven - 7/24/11 at 1:33pm