Todd,
I think the tornado's new sail plan takes it out of B Class. But then the tornado sport is only rated marginally faster than the N20(and that is with the best sailors in the world setting the rating) making them pretty equal boats. It's not the beam it's the entire package.
What makes the F18 class work well is that most boats are within a narrow performance window. With what you are proposing the boats would be all over the place. If you want even class racing you have to have an even class of boats. No matter what you do to an H20 you are not going to get it to compete with an equally equipped N20. The hull designs are on a different level.