Im 5'11 and 140 and I ride a 154 malolo as my powder board. I have no trouble floating on it. Because of the taper and setback it can be turned really quickly. Ive had mates who weigh a lot more than me ride it as well with no probs. Its only in deep pow (1.5ft+) that i start to get float issues. But the malolo is not an all-out powder board either.
If you want a fast, tight turning powder-only board for the trees then get a fish. I cant find any other board that compares to it for that purpose. The compromise with the board is that it doesn't hold an edge very well on groomers, they don't have much pop due to the short tail, and they can be difficult to traverse with.
If you want pow only, max tight turing board: fish.
Or if you want to compromise slightly for better all-round performance get a malolo or lib tech snow mullet.