lots of float, and tight turning, id look for something with taper and rocker, both make big boards turn quick. I have a libtech snowmullet and it is a great shape, the birdman is the next evolution. My 165 is super maneuverable, and playful, a 170 birdman looks like tons of fun. The smokin pinner is supposed to be similar. I've riden the charlie slasher and its fun in the pow but is a bit stiffer then the mullet and has flat camber instead of rocker, making it less playful. A hovercraft or fish are going to fit the bill too but are even more directional.
Since you already have a good all mountain board don't compromise when getting a powder board, you will be rewarded when riding a true pow shape when the snow gets deep.