If he builds the carb and tunes in correctly the Q-jet will make more power on a factory intake than the Demon.
If he uses an aftermarket dual intake with both patterns the Q-jet will still make more power as it lines up directly in the center of the plenum areas vs the square flange Demon carb.
If the q-jet gets it's butt kicked he doesn't know how to build and tune one effectively.
I've been on the dyno scores of times and been asked to do such tests, and to date NOTHING we've ever bolted on, Holley, Demon, Quick Fuel, custom built Holley, etc has outran my 1977 Pontiac Q-jet.
I even did that test back to back in 2004 when we did the HPP and Popular Hot Rodding Engine Masters articles testing the new KRE heads. The Q-jet ran quicker at the track a few days later as well.....but of course NO ONE involved with that deal wanted any part of those results!.........