If it will be your ONLY board then I personnally would lean to the 150, however if you still have your 156 then i would get the 146.
Based on what you wrote though you want the 146.
The raduction boards dont "feel" like bigger boards, they feel small. They just ride bigger (float, effective edge)
ANyhow based on evrything you wrote I would go with the 146 and ride the custom on days when I am trying to go really fast.