Thought I'd through my two cents in since we seem to be really similar:
I'm 5'11 and I weight around 170-175lb. I have a K2 Turbo Dream 159 as my pow dominant board, but I recently just got a Lib Tech Attack Banana 157 as a park dominant board. Lib Tech's are really flexible, so your weight with that short of a board would probably equal to the same thing I'm looking to get out of my Attack Banana, which is park dominance. I'm not exactly sure, but i'm fairly certain the Banana Magic is a little more stiff than the Attack Banana and Skate Banana, so if you want Pow/freeride dominance I would go with a larger size
Attack Banana is a bit of a strange choice for a park board. It certainly is fairly stiff - about the same as Banana Magic and T. Rice actually (all of them much stiffer than the Skate Banana).
In order of float it is roughly Magic>Attack>T. Rice because of the extra rocker/more mellow camber in the profiles (Enhanced>EC2 BTX>C2 BTX).