I got the Prophet 100's in the 172cm length and skied them on about 12 inches of powder at Alta...Great! :)
They float well, but are still similar to an all-mountain ski on the groomers back to the chair. I have 80mm wide Assassin Pro MTX, which have the same titanium reinforcement layer, this makes the Prophet 100 stiffer than I expected, but this functions well. I like the stiffness when out of the powder. Ski is still all mountain enough in performance for me to keep them on when not in deep powder.
I have three pairs of Lines now, and am making good use of the Rector binding, which is very easy to switch between ski's, don't forget to buy some fatty brakes to fit this super wide ski.
I happened to ride up the Alta lift with someone who had the Prophet 130's, which only make sense in deep powder. If you want a great powder ski that is still manageable on non-powder days, the 100's are the way to go.