My concern is mixing sailors with different skills not boats with different speed.

If you are sailing in a fleet with skilled sailors you know what to expect in tight situation, but if have have sailors that can't handle the boat or are unsure about the rules you will run into problems. Hobie used to have a, b, c fleets where you could start you sailing career in c-fleet and then gradually upgrade to higher fleets. It is no fun to start with your roboust Hobie 16 in a fleet with expensive and fragile carbon boats....

/håkan