The Raygun is a sweet board for the price. I fully expected it to cost more when I demoed it. One thing about it though, it has an extruded base so it will lose speed when the wax is worn. Just wax it more often if you want to maintain the best speed from it. The Raygun is going to be great in powder because of the All-Terrain rocker. On groomers, it is really decent. The weakness of this board is the stability. On steeps, it has chatter. It is a mid-flex board that costs under $400, so I don't expect much different from it. Great board
K2 Raygun Mens Snowboard 2011
If you want to invest a little more, the Darkstar is also an excellent choice for you. The Flat camber is a great design and carving on it is a blast. This board is also around a mid-flex, but the camber profile of this one makes it more stable on the steeps. Not as strong of a powder performer, but still much better than a positive cambered board.
K2 Darkstar Mens Snowboard 2011
If your boot size is below 11.5, then you can go with either the 156/157 or 159 on either board. The longer size is better for your weight, but the smaller one will work. Smaller will be a little more playful while the bigger size will be a little more stable.