I've owned two 1980s and one 1981. Although my friend 's '81 had an air flow issue above 6K, my bike pulled as strong as the two PD-carbed bikes. Odd how it seems to affect only some of the CV bikes; then again, people tend to baby these old bikes and many people probably do a lot of short-shifting, keeping their bikes out of the upper RPM range.
Notwithstanding all that, I would much prefer living with the CV carbs over the PD mechanical slide carbs on a daily basis. The CV design solves (or at least minimizes) many of the disadvantages inherent in the mechanical slide design. Really, the only significant advantage the slide carb has over the CV design is increased air flow; even when the CV's butterfly valve is at horizontal position it still impedes airflow to a certain degree, so all else being equal, a slide carb will flow more air than a CV carb of the same size.
Of course, that one main advantage of the mechanical slide design is offset by its many disadvantages.
Snapping the throttle open at low speeds will cause a stumble due to the momentary lagging of the fuel behind the faster-moving air flow.
The slides are exposed to engine vacuum, which causes wear and stiction. To overcome this, a very heavy return spring is needed. Working the throttle against this heavy spring action can get quite tiring after awhile.
Because the slides need to be lifted mechanically, the carbs need to be tall. The slides need to be able to lift the full height of the Venturi, and the jet needle has to be longer than the Venturi height. Then you still have all of the linkage that must ride above this setup.
With all of the above, it makes it tough to design a rider-friendly throttle action. Either a very heavy action due to the heavy return spring or very long twist grip travel.
The CV butterfly valve design solves these and other PD shortcomings, especially low speed throttle response. The constant vacuum in the Venturi allows more precise fuel metering, and the butterfly design allows the use of several low speed bypass openings that produce a smoother transition from idle to part-load.
After about a 1/2 hour of fighting against the heavy return spring and the very long twist grip travel on either of my 1980s, I was always glad to jump back on the CV-equipped bike...
