As it was stated above, if you shorten your arrows make sure you do not lighten the arrows to below the manufacture's min arrow weight.

Other then the weight issure, shooting shorter or longer arrows will depend on your setup. If your shooting custom arrows, or light splined arrows, then longer is not always better as you could get alot of flex in the shaft. Shooting shorter arrows will lighten up the total weight to enable the arow to go faster, but the cost is usually the stability of the arrow. The arrow is stabilized by the fletching and depends on the distance to the tip on how quickly this stabilation can occure. The shorter the arows, the more radical a (lets say) 2" wobble (whcih the fletching straightens out) will be over the longer arrow. This is also why vertical shooters can out score crossbows at major compitions (longer arrows).

Best bet is to try, then see what your bow shoots best, but for me, longer was better and I shot 2117 & 2216 arrows with an Excalibur bow.