I don't know if you're still interested, but I'll be able to give you a review on the 159 Westmark 2009 next week when I ride it for the first time. I'm 6'4" 165lbs sz. 12 and I found that 155s were just too short, but I've made 159 work well for me. Length, as long as you're in the weight range, is rider preference. Like you I'm hoping the length will give me added stability. Stay tuned for next weekend's review...
Board: Arbor Westmark 159 (2009)
Bindings: Flux Super Titans (2009)
Boots: DC Field (2009)