Thats quite a range of needs for one boot, Matt. I think you can pull it off, but as with all things, when you try to make one item work for several applications, there will be compromises.
The main question to ask is this: When is a boot most a matter of life and death? I think thats pretty clear: when ice-climbing (Ptarmigan Ridge! Thats a pretty fearsome route!). So Id start by looking for good mountaineering boots, and then see how to make them work for your splitboarding. If youre using leather boots now, then I think youll love a pair of Scarpa Omegas ($369; scarpa.com). These are very trim, plastic-shell boots that are great on ice, snow, and mixed routes. La Sportivas Trango Ice EVO ($380; sportive.com) might work well, too; theyll be a bit more flexible than the Omegas.
How well those will work on a splitboard is an open question. They certainly wont work as well as the Scarpa Matrix, an alpine touring boot ($560). But then, I dont think the Matrix would work at all as a serious climbing bootnot enough feel," and too high. They are fine for moderate angle stuff, but when youre on mixed terrain or front-pointing, I think youll run into problems. And who needs problems at a time like that? I dont even think youd find it very comfortable; even when loosened, it will still want to push your knees into a partially bent skiing position.
I will say, theres a good reason for all these sport-specific boots. To get the most performance out of crampons, a split snowboard, skis, or whatever else, it really pays to have a foot system (i.e., a boot) that does the best job of transferring power to whatever it is that is trying to grip or slide across the snow/ice.
So, Id start with the mountaineering boots. But be prepared to take out that second mortgage for a pair of AT boots as well.
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