Back in the 70s there were a few people that used bigger carbs for better mileage.The thing is,there is a lot more to mileage than carb size.What makes a carb work well or accelerate quickly does not usually apply to better mileage. Holley double pumper carbs are "known" to have poor mileage,why?
Because the guys that use them yard the carbs wfo all the time,because they make power.Power burns fuel. Accelerator pumps toss in a lot of raw fuel to compensate for low intake velocity,double pumpers are self explanatory.
If your fuel/air ratio is correct,you do not change speed,do not go up hills,then your mileage will be about the same with all carbs.Drivers kill most of the mileage with aggressive advance of carb linkage,its all just math and the efficiency of the carb and its systems to circumvent our poor driving skills.Take the accelerator pump out of your carb and your mileage will increase,drive ability will be terrible