I haven't played with too many different kinds of bows, but I have heard and read that you want your arrow to extend 1" past the most forward part of your rest when you are at full draw. I'm pretty sure this is for safety's sake so that the arrow has no chance of being drawn back behind the rest.

Just for discussion, I have a MQ-32 @ 29" and shoot a 29" arrow that extends more than 1" past the rest. I could cut it down just a tad, maybe to 28.5" but it shoots fine the way it is.