I have the Senn 590's and they are very light and comfortable. I've read several other threads which indicate the 570/590's are more comfortable then the 580/600's line, but I only had the 600's on for a short demo, so I can't really comment more then saying that they did seem a little heavier IMO.
Headphone I can stand for more than 1 hour
Every headphone I have ever had starts to drive me crazy after 1 hour. I started with the Sennheiser HD 414. Warm foam cushions and push too much on my ears. Tried the AKG K-1000. Too heavy and push on the side of my head. Grado SR 325 - too warm. Why can't anyone make a headphone that sounds good and one I can use for a couple of hours? Have you found a comfortable one yet?