Torque
A certain amount of back pressure is good for torque and a Rocket III with slipons, tuneboy and triple filters has plenty. I'm sure you'll get more high end HP with the Jardines, but on the R3T who cares? Nothing like short shifting first and shooting up to 85 in 2nd gear!
The "empty" box is a resonator and in conjunction with the D&D's gives the bike a nice deep "throaty" sound. I'd like to hear D&D, Jardine, and Raask side by side. Sound clips on the internet are useless.