/6 Exhaust: Dual or single? Your thoughts

For many years now, my 70 challenger with the 225 SL-6, has been running very efficiently with the super 6 set-up, mopar elect. Ign. Orange box, high output coil, open element 14x3 K&N filter. As for exhaust system Hooker headers 3 into 1, 2.25 aluminized pipe, real duals w/"H" pipe crossover all the way to back of car, dual glasspacks and chrome cuda style tips under rear valance. As far as I'm concerned it sounds great and if pick up efficiency and or HP's along the way, so be it.