Tech-

I have had carb size/configuration discussions with hundreds of different people of varying expertize of doing engines------

A double pumper has progrssive linkage to the secondaries and alltho they will reach wot at the same point, they are not equally open front and rear-as you drive within the part throttle region, the bores aren't equal.

Double pumper carbs are easier to tune for high performance driving altho vacume sec are easier for pussy/check writer drivers that want to say (insert various quotes here) I got this much horse power--------yep on a dyno wot -----but can you drive it in any of those upper rpm/hp ranges?
A double pump carb can be set up ( I like the 800/850 sizes) so you can drive higher range on just the primaries at a more effient fuel milage/mixture and yet have the secondaries come in the last part of the throttle range without needing to be wide open and/or not getting it til later -the mech sec carbs have the advantage of running richer jets toward the top end and also added power valves to make up for leaner cruising on pri.

I have done thousands of set ups for various vehicles ranging from Grand mas car to road racers, drag racers, hill climbers, etc------I aim for drivability range in the street area and record setting results for the racers-------