I can tell you with 100% certainty that a 14.5" Bushmaster Barrel with a permanently attached Phantom or Vortex flash suppressor IS slightly OVER 16".
Bushmaster offers them as an option for pre-bans, and I owned one as well.
As for the 14.5" vs. 16", I was always quite strongly on the 14.5" side of the fence, until I bought my first 16" mid-length barrel. I never saw any difference in performance or accuracy between the two, and all the "velocity" stuff is pretty much just figures on paper as far as I'm concerned, BUT being able to swap flash suppressors, change front sight bases, add free float/rail tubes WITHOUT the expertise of a gunsmith has been the deciding factor....
On the other hand, if you just want an M4 clone, then those things probably won't matter to you, and for that, a 14.5" IS the one to have.