Generally speaking, in a given design you will find a longer bow to be more forgiving, and a shorter bow a little faster. There's a point where you loose more than you gain either way--too long, you are loosing performance without gaining much if anything. Too short, you get stack, finger pinch, instability, etc. You won't see serious target shooters using a short bow.
If you plan on only short shots, it probably won't make a difference. If you plan to compete, or take longer hunting shots, it will--unless you have perfect form and a perfect release.
That's my 2 cents, FWIW.
Chad