I bore you but you keep me excited with all this unlogical stuff you say all the time.It is personal preference to an extent, but physics works for everyone the same,longer crank=more leverage=more power.Your problem with run ups is weird too,what if the run up is actually a steep hill?you will have hard time(harder) to even get to the obstacle with 165mm.And clearance isn´t an issue with modern geometry frames either.Oh,most elite riders use 175mm cranks,I think they know thing or two about clearance and run ups.But you can use whatever you like,but it doesn´t make it right or logical