gas mileage Mechanical vs Vacuum Secondaries

yes, when you're on and off the gas, I can see mileage suffering when the accelerator pumps are constantly pouring fuel every time you mash your right foot....that's kinda why i asked about steady state driving, just cruising down the interstate for example....
i understand the secondaries would be open (mechanical), but I guess I can't see that in itself burning more fuel (vs running just off the primaries, which would have to be open more to be running the same speed down the highway)...

maybe my real question is, is the engine more efficient using two small venturis vs four larger ones (that aren't open as much)?