One factor most fail to mention/consider on this, is if the single and dual carbs are the same size or not. In general a bigger single can flow more than a pair of smaller carbs at hi rpm WOT. My surprise on past Ms Peel was going from single 34 mm Miki to dual 32 Amals was the loss of her top speed power. But the response was slightly duller at slow speeds, below 60 mph with the bigger single than the 2 smaller Amals. Most detectable on THE Gravel as I had to twist further-faster-throttle to break loose with the Miki than the 2 Amals.
Of course the split manifold is an issue, just ask the the Big Vtwin crowd. I must of lucked out on Peel because I got like 15 mph higher speed on the 34 vs 2-32's. If not trying to spank new sports bikes I prefer the smaller dual carbs for the better low end up to legal+ speeds on my factory Combat but I liked/loved the bigger single for over the ton thrills on a special built to strain things.
There is another aspect to consider in dual vs single, the size of the air plenum, if a carb only feds one jug it takes a rather bigger carb to supply it at top end than if a smaller carb is used with a bigger manifold volume to feed two or more jugs. This is why fuel injected stacks were so big per jug in past racers and why smaller throat fuel injectors with big air boxes are used in the inline 4 sports bikes nowadays. Length of manifold can make up some speed-momentum of intake charge at lower rpms on a bigger carb that can fully feed at top end.
And another thing, if the head ports are 'too' big, like the factory Combat, the intake velocity is sluggish to fill jug with turbulence so smaller carbs can help response d/t a bit faster mixture speed compared to a bigger carb on same head/cam.
Comstockt-Fullauto head use smaller better shaped ports to get its advantage over the factory heads so could get away with bigger carb and still kick ass down low and keep on increasing as rpms rise.
I my case I'm sticking with smaller dual carbs for the response on a stock Combat but on my big block Peel, with big ports and big cam I'm going with a bigger 40mm single. There are many reports on other lists of the joys of putting on a 32 single Amal over the duals for normal everyday ease and response short of land speeder use. Its a better more efficient mixture feeder when getting the double sucks on each turn, just as the initial poster described.
What would be the cats meow, Quadrajet like single carb with two barrels with progressive linkage, small barrel down low spunk and no end to the top end flow as the big throat opens up as wind spreads your grin.