Concur on the Bose X ($1000) being overkill in the jets. We have several of the early model CRJ's that have very noisy windshield wipers, so I prefer the X in these planes.

I also use the Clarity Aloft Pro ($750), very VERY light, doesn't touch your head anywhere except over your ears (like sunglasses). I ordered custom molded earplugs, and that makes them an excellent jet headset. Note: not recommended for noisy turboprops, no ANR either.

For $600, I dunno. I did buy a DRE ANR 6000 headset ($300) that I really like a lot for the money. Much like the David Clarks in size, weight, style, etc.

http://www.flydre.com/headsets.html

I'd probably be tempted to try the LightSpeed Zulu headset ($850)

http://www.zuluseries.com/