Another data point for the books: Yesterday's backcountry skiing mission turned into an absolute slog with a partner who relies on intervals/hiit. I estimated 2 hours up, but conditions and straggling partner turned this into 5+ hours. My partner went down hard about 1.5-2 hours in. We had no effective bailout option but to keep going as trying to bailout early would have been a far worse option. I tried to talk him though it, I tried to get him to slow down and take a "slow and steady" approach, but every time I put my head down and focused on maintaining my consistent zone 2 pace for a few minutes , I could hear him breathing super heavy and I was 100+ yards ahead of him. He had no sort of management or self regulation for a consistent conversational pace.
Make sure your partners are on board with this type of conditioning or you are going to run into problems.