No hard and fast rule here. Where is your rest mounted? And think ahead as to whether you may ever relocate it more forward. Generally speaking you would want the end about an inch forward of your rest.

I usually just cut my arrows the same as my draw length. This allows me to mount any rest I so desire and work with any bow I want to shoot.My draw length is 27" and all my arrows are, too.

Don't get concerned about a speed increase with the shorter arrow unless it allows you to shoot a lighter spined one. For instance, if you shoot a given arrow at your draw length (27.5") and want to gain more speed by cutting an inch off of that same arrow you will only gain about 2 fps because you're only removing about 8gr of arrow weight. You're better off to just shoot the longer arrow and be done with it. Just be sure your arrows are spined properly for your setup.

If you are a more experienced shooter then you would know that anything long enough that you don't draw it past the rest is fine, but then if so you wouldn't be asking this question.