What say you about Prop Cupping

I was considering getting another (emergency spares) set of props for the boat.  I've got Michigan Dyna-Quad 18X21 props with 1.5" shafts.   When looking at new props, I noticed the option to have them cupped at various degrees (light, medium, etc).  I have no first had knowledge of the benefits/drawbacks, but a bit of reading seems to indicate the cupping might give you a little better bite out of the hole, but maybe a little less speed on the top end.  What say you?  Anyone have any experience/opinion with this?  Any impact on fuel burn rates, other issues/benefits??


Thanks,


John