A trick for building VO2 max and metabolic rate is to emulate conditions of altitude as much of the day and night as you can, and to do concentric exercise in short durations.
Emulating "high" altitude (for example, Aspen) requires 15-16% oxygen in the air you breathe (which can be achieved with 5-6% CO2).This isn't as hard as it sounds if you make your own rebreather with sufficient dead space (similar to an elephant's trunk or a giraffe's neck), or add a little CO2 from a tank to your air supply.
You can prove this works for yourself if you can measure VO2 max. Or if you're into studies (which I'm not, too many uncontrolled variables, and I'd rather prove it for myself), there's this:
@4a55, to your question, the type of exercise you do can be guided by your ability to do it at conditions that emulate very high altitude. If you can blast a 1K at (emulated) 9,000 feet, then rock it!
I think you'll be amazed by how much more benefit you achieve from the same level of exertion when done at emulated altitude, even for much shorter durations. My experience: emulating altitude before, during and after exercise, and as much of the day and night as you can, even when sleeping, will give you the greater benefit.
I think you're right about high VO2 and less fat. The greatest challenge in climbing extreme heights is getting emaciated, no matter how much you eat.