You've got two things going on that sort of offset each other. With the higher brace height, you have a higher peak weight at full draw. With the lower brace height, you have the arrow being pushed by the string a little longer. Within the normal range of brace heights, my understanding is that you will get a little more speed out of a lower brace height. You also will get a little more noise and vibration. But you would really need a chrono to tell, and I'll bet the difference, within the recommended max and min brace heights, which is probably less than an inch, would be only a couple of fps. The general rule is to reduce brace height until you start getting noise and vibration.