I find the Edelbrock catalog to be informative on this subject. Of the many "crate" engines in the catalog are two 350 cid SBC units that are identical except for the number of carburetors. The single 4 barrel unit makes more HP and torque than the dual quad unit.
Since they both come from the same source, we can assume that both are in optimum tune, an apples and apples comparison.
I have asked people why they run dual quads if a single quad is more powerful and the answer is always one about aesthetics.
So it appears that the answer to questions about multiple carburetors is "Do you want impressive power or impressive (to some people) looks?"
