All of the Webers have secondaries, its the progressives that you are thinking about where you can floor it and open it up. Progressives are the ones where the primary venturi is smaller than the secondary (as in 32/36). As far as sustained highway cruising I would think economy would be the same as the throttle will be wide open on both of them. Its the city driving where you go in and out of throttle and you do a lot of idling where you'd see a difference.
As far as a CVCC engine is concerned, a Weber is a tradeoff for fuel economy and efficiency anyway because you don't have the 3rd venturi to work the CVCC chamber. Someone on the 1g Honda board said that Oscar Jackson himself would still do a performance jetting on the CVCC carbs for a price, but this was a few years ago. Not sure if there was a Canadian non-CVCC head to fit the later EK/ES series engines, but that might be worth looking into...