Well.. an easy guage is to find something that hits you at CHIN LEVEL.  From there go taller for SPEED/POWDER and shorter for SPIN/JIB/FREESTYLE.  WIDTH of the board is really important too.  An average joe has no business getting a WIDE sasquatch board (26cm+ waist width) for all-around use; the smaller your boot size the narrower you need to go.  Width is more important than length.  Look for about .5 to 1 inch overhang (soft boot feet when placed straight across board with feet shoulder width apart) equal heel and toe for best edging performance.