I also have an ES with exhaust pipes sticking down far more than is cosmetically appealing.  I also wonder what length I should cut them before first flight..  I would think that oil on the belly could be delt with by collecting or returning excess blow off.  The other issues that might be relevant would seem to be 1) drag, 2) heat transferred to parts of the cowling, 3) noise.  Are these the main issues?  Any thoughts on how to cut the pipes to balance these issues?