Well, I can only speak as a 56 Super owner but, I will give my 2 cents. If you start out in "D", acceleration is very slow up to about 30 mph (it does get there but, slow). The dyna only has one forward gear in "D" and from a stop, it is akin to a manual tranny taking off in 3rd however, if you start off in "L", takeoff is much better and I can keep up with modern cars. I even passed a 1995 Ford Fiesta once :).
The way I drive my car is, take off in "L" and switch to "D" at about +-30mph or so.