I use as much helical as the shaft will allow me to use.

The more helical an arrow has the more air the feathers or vanes catch and the faster they stabilize and spin the arrow.

Of course this is assuming that a person can get away with this much helical. A shoot through prong rest will need straight or about a 2 degree offset to clear the prongs.

Look at these and you can see that the vanes go from one side of the shaft to the other side in 4 inches. These are in the classaifieds BTW.