If I were living in Sapporo and trying to have the Prior quiver killer, my vote would be for an ATV in the high 160 range, for the trees and powder, followed by a 170ish WCRM or an FLC for the groomers.
I find the 4WD has too shallow a nose profile and too narrow a waist width for really aggressive powder and tree slashing, and this is coming from someone who has had to regularly romp through trees and powder on a 164 Atomic Proton...
I never said that I was a quick study....
A carver's haiku-
My board's a scalpel,
To carve deep ruts in the snow,
Is my destiny.