on a stock stroke 440 based combo, especially in a heavy car, if i were to be inclined to use a downleg booster carb, i'd stick with something that had a 1.425-1.450 max venturi diameter.

going from memory here....
Mighty Demon 750 = 1.400
Mighty Demon 825 = 1.425
QFT Q-750 = 1.375
QFT Q-850 = 1.400
QFT Q-950 = 1.450
QFT Q-1050 = 1.590

it can be a challenge to get a large bore, downleg carb to leave hard with a 3.75 stroke motor in a heavy car.
also, sometimes the shift recovery isnt that great either.....although they often make good power on the dyno.