Do you really think the 158 won't be that much easier to whip around in the trees? Honestly that is something I am really hoping for, in addition to being able to ride switch in powder more easily and throw in a quick spin or log ride here and there.
Look at the K2 Ultra Dream.
I think this might be more what you are looking for.
If I could afford to have a freestyle specific powder board I would own one.
Tips that will float for days.
If it is anything like my gyrator you'll never sink.
The trade off is probably edge hold and responsiveness on non-pow days.