Tune, Cam sync, Cam orientation, arrow spine, tune, all effect the final speed.
In my experience when I get a BowTech setup and tuned I have been slightly better than the BC all things considered, and at the very least as good. I go over everything, or take it to someone that is experienced in tuning Binary Cam bows and see what they say.
Sounds like your tune could definitely be a factor. You can Not push an arrow sideways as fast as you can pushing that same weight arrow straight down the middle.
Most Destroyers I have had my hands on or I am aware of have been slightly better than the advertised IBO.
Dan