On the whole "size matters" thing; I crewed on a Blade F16 and had no trouble getting under the boom, I think it is about the same height off the tramp as any F18, Hobie 18 or Inter 20. I'm 5'9, not 6'4". Anyone over 6' is going to have trouble getting under any boom if crewing and up close to the mast.

The big advantage to the F16 is indeed the light weight, not just of the boat, but also of the mast when it comes time to step it. The other advantage is you can race it solo if you can't get crew or the wind is light or what ever. To race the F18 you MUST have crew, it's in their rules, and it is nearly as heavy as the N6.0 and Inter 20, If you are not going to race, you can sail them all solo, of course.