Well, I recall from 2e (which was originally from 1e, I believe), the D&D broadsword was a medium weapon, speed factor = 5, damage was 2d4 vs. medium/1d6+1 vs. large.
So, for a 3e representation, I guess I would just go with a 2d4 medium weapon with possibly 2x/19-20 crit. The 2d4 makes it...