The 4807 168 is my light powder and chunky slushy dream board. The 178 is heavier and harder to throw around in the trees it is however great in deeper powder. the short stiff tail on these boards is the key to their carvability. they still sink in the pow but will hold up on the groom. when carving the nose is forgotten they become a much shorter board. If you are having trouble carving them you likely have the bindings to far forward. mine are all the way back and I am 6'4" 275 lbs. it holds and rails quite well for me. I actually prefer the 168 version on soft groomer days where it gets pushed up into piles. extremely versatile board.
That said, you asked for a powder board that would only be on the groom briefly . I would have to point you toward the nitro swallowtails or to the winterstick. the difference between the two is nitro's long straight sidecuts vs the winterstick's taper. wintersticks are miserable to ride on the groom and nitro's are doable. the nitro is very flexy and soft and wouldn't work well with hardboots longevitywise but you can flex the big 196 into a very tight corner just by squeezing the knees. they ride as small as you squeeze them. on a wide open untouched powder field from a helicopter I would take a winterstick.