I was actually quite surprised at the comfort of them after seeing a lot of people complain about them. Personally I find the HFI-680's very comfortable, the clamping isn't bad at all, and it does relieve some more pressure if you extended the headband all the way which I've done mainly because the way the drivers are targeted towards the bottom. I guess it depends on skull size and what people are used to. A measuring band around my skull from back to front is 23 inches if that helps. I find these cans comfortable, my whole ears fit into them, the vinyl material feels nice, they are light, I can wear them for hours. This is coming from a guy that is used to wearing ATH-AD700's and DT990's all day too.
Actually if I had to rate it, I would say the clamping is perfect. Just my opinion though, I don't want to over-promote them to then get your expectations too high and then you find you don't like them.