Shooting that extra inch of draw length will give you approximately an extra 10 feet per second for sure,and the added draw weight will definately pump up the speed as well.
BUT----I am a little confused on something.Dont take this as an attact,an insult or anything but how can one shoot 28" draw and 29 just as well.Isn't your anchor changing with the different lengths.I always tell guys to get comfortable with a certain draw length,and maintain a consistent anchor .Besides,isnt accuracy more important then speed if you plan on hitting anything.