This is probably the only situation that would warrant me considering the Bose Quiet Comforts. Though the audio quality in general isn't anywhere near as good as anything we typically look at in the price point, I have to hand it to Bose that they are extremely lightweight and comfortable, and the noise cancellation is fairly well executed, although I don't particularly like active noise cancelling, since it makes me feel funny (your head feels a bit like a vacuum, and you feel very slightly unstable). IEMs might actually produce better sound at your price, but I can't see them being comfortable for a long plane ride.
I'm a little on edge for the HM5s, I don't think I'd wear mine on a plane ride just due to the bulk.
Just my 2 cents.
Edit: Since Bose is a more mainstream brand, it's not too difficult to find a large electronics store where you can try them on. I've run into a Bose display quite a few times.
Edited by Rickstahful - 1/24/12 at 6:58pm