yes, it's just weird to think of myself riding a 159 on powder. I mean, I used to ride a 158 for freestyle only. But yes, I guess the rocker/camber allows to downsize quite significantly.
Rockered boards will float much better in the pow than any cambered deck. Plus you don't need to adjust your riding for pow ie, stance setback/lean back...
Also, don't just concentrate board size purely based on the length. While there is a generic length range for your weight, you should always consult the board's weight scale. Take the Machete for example. A 158 Machete supports the weight range of a 156 Turbo Dream.
Off your list, I demoed the Custom FlyV... I loved it. Very versatile board with medium flex. 162 is the size for you in this board.
Burton Custom Flying V Snowboard 2011
I have some other suggestions for you. Since you sound like a powder/tree junky, I actually suggest stiffer boards.
Ride Highlife: I love this board. Stiff with variable rocker. The rocker in the nose is more pronounced and mellows out to nearly flat in the middle and subtle rocker out to the tail. This is great for powder. The stiff flex also makes this a fast and stable board on the steeps. 159W for you in this.
Ride Highlife Snowboard 2011
K2 Turbo Dream: This is my new board this season. I bought it because of what it offers for the price. I am going to Tahoe next week and was in need of a board that will perform in powder, but also ride sweet back here in the Ice Coast. Mid-stiff flex with K2's all-mountain rocker: Flat camber between the bindings, mellow rocker through tip and tail. This year, K2 added Harshmellow to the board. I'm a big fan of Harshmellow for two reasons: 1) It makes the board damp (stability is a common problem with rockered boards) 2) It makes landings off of jumps/drops pleasant. I haven't experienced a cliff drop yet, but I did jump around on this thing. Landings felt good coupled with my damp bindings. 160W is the size for you.
K2 Turbo Dream Mens Snowboard 2011