RE: Is shorter better?
First you need to mention what bow you have!
If the track is short...you ARE stuck with short arrows. But if about 80% ofa 20"arrow is supported..yes...it is better to shoot longer arrows.
Not to mention the extra weight, which is a good thing...the longer arrow will fly better, e.g - hold its trajectory better.
But if only half of a 20" arrow is supported...
The BESTthing to do...especially since you HAVE them......is to shoot them...see how the 20'ers shoot!
Mike