I have experimented with my chrono and varying arrow weights string weights, silencers-you name it. For me, weight and speed are completely interdependent-heavier is slower and lighter is faster, whether the weight is in the front or the back or even on the string, has not mattered.
The question is-how much slower or faster? Going a little heavier always made sense to me because the loss in speed was negligible compared to the gain in 'power' or 'potential penetration' you can give that any physics name you like.
As far as trajectory is concerned; at 20 yards I personally have not noticed much change.