It seems to me your after a board for the "one day" of deep powder and wide
open runs. Those days are rare so I'd get a board that works for daily
riding. At 172 cm you might as well try skis. [sic]

Perhaps you should actually try boarding in deep powder (not
hard-based resort eg-fluff) on a board which is suited to your weight
& style. You'll ride much faster and with much less effort and your
thoughts of skis will vanish.

Obviously it depends on your weight and the board style. Light-weight
agressive riders like me can get away with about 170 in deep powder;
the majority need and use something longer. People tend to edge a few
cm more when it's very deep.

In my experience board length makes little difference to turn ability
in the trees, which is just a technique issue.

Obviously Fish and related board lengths run differently.

phil