I have used the Scarpa Phantom 6000 on many glaciated mountains up to 19.5k ft, as well as ice climbing in Colorado. The only complaints I had were 1) the liner was unforgiving size-wise if you changed soles and 2) the zipper was faulty (broke on the 1st pair, and the replacement pair that Scarpa was kind enough to swap free of charge post warranty). While you can fix the zipper temporarily on the older version with pliers and Tizip (or any waterproof compatible zipper lube), the fixes never seemed to hold. The old zipper was stiff and wrapped around the calf at the top making it difficult to zip straight up, which is partly why (I think) the zipper had issues. But, in the new 6000 HD, the zipper no longer wraps around your leg, which makes it almost a straight pull (some slight twist / angle). The zipper itself is also much easier to pull closed (even before applying zipper lube). Moreover, with literally less zipper to zip, you have that much less "point of failure" space. The new liners are more flexible and seem slightly more forgiving with custom soles. So far, I'm quite happy with the changes.

Walking in them is slightly easier than the older version, and they feel slightly lighter. I have yet to use them on a mtn, but so far, the changes in the 6000 HD take the boot even further away from competition.