There's so much misinformation above about formula class, most people I know that
race formula avg. income, fit but not super strong or big (I'm 135 lb, 5'6"),
there was a comment about fins, there's one fin that currently in demand 'Kashy',
the rest are reasonably priced and you can buy many high quility customs used,
it's not the latest fin that's going to win you a race, it's your skill!
also Formula Experience boards would reduce usable wind range of the boards, specially
light wind by couple of knots, so I wouldn't do it just based on that.
We just had a great race in Miami with 2 classes, Formula and Kona, both classes
had a great time, but even in the light winds Formula plained thru most of the races.
check out, www.miamiwindsurfing.com