Yeah look up "snowboard top speed" on this thread and you'll see many discussions about it. Nowhere does effective edge have anything to play into it.
The question is: are you spending time on the hill going straight down as fast as possible?!?
Well my question is more towards, which one would "plane" more.
If your on a hill then a flat spot, would the one with longer effective edge would plane more.
Sorry for the confusion.