[Oldsguy]

Normally under regular driving habits, quadrajets give better fuel economy because their primaries are smaller than most other carbs, they are called "spread bore". Most other carbs like Holleys are called "square bore" where the primary and secondary barrells are the same diameter. But, if you get into the gas pedal a lot, then you may see poorer fuel economy with the quadrajet because the secondaries are larger, much larger than the primaries. If all other things are equal including carburetor cfm rating, then your performance will probably be about the same between carburetors with a little better throttle response with the quadrajet because of the smaller primaries, especially in the lower rpm range. You might find a little better overall driveability with whichever carburetor is newer and more recently rebuilt but that is something that can be corrected in the older un-rebuilt carb. Lots of variables.....