Im 5'10 165 and ride my 157 banana magic for pretty much the same thing as you, i hit park jumps and natural hits as well. And my pow board is a 158 charlie slasher.
157 seems about right for all-mtn style riding for me. But i just got a 151 for learning to jib and just farting around, it isn't as good for going fast though.
Good gear doesn't make you better; good gear makes it easier to get better