If you ever climb out of the saddle or think you may someday, also consider your out-of-saddle position when chosing a stem length. If you get the stem too short, you'll feel cramped out of the saddle. Your knees may come within striking distance of the bars. You may be climbing with your shoulders almost in front of your hands, resulting in poor balance and control.

Also, make sure your bottom bracket to saddle setback is right before thinking about changing your stem. If you get that right, you should be able to hold your upper body in balance on a trainer while padaling if you let go with your hands (at least briefly).