OK I am just taking a stab at this but in >10 knots a RS:X is faster upwind (centreboard) but formula faster downwind. 10knots + formula (once planing).

Is that about correct

If so why sail an RS:X over a formula if you are obviosuly not going to get into the Olympics?

Are the fleet sizes comparable?

Xtra heavy? (18Kg)
Xtra slow in light winds?

Do a search on this site and you'll probably find out why you would probably be better off with either a longboard or formula, depending on your needs and budget.

If you are not planning to race in the one design division of RS:X then formula will usually be the better option, RS:X will only out perform formula in sub plaining conditions.

interesting info from the ISAF web site in the current formula class rules:

C.5.1 FIN
(a) LIMITATIONS
A fin shall not project more than 700cm below the hull measured at 90
degrees to the fairline of the underside of the hull.

C.5.2 CENTREBOARD /DAGGERBOARD
(a) LIMITATIONS
A centreboard or daggerboard is prohibited .

C.6 RIG
C.6.1 MAST
(a) DIMENSIONS
minimum maximum
Mast length measured from the fair deckline .......................... ... 6250 mm

It seems that you are allowed to have a fin that is longer than your longest mast.

Formula race in 7knots and above. RSX racing in 2 or 3 knots. Formula is faster in all conditions except 2-6 knots.
There are large fleets of Formula racing in NSW, with lots of divisions - Youth, FE+, Grand Masters etc...
RSX is specifically tailored to Olympic hopefuls.

www.storm-riders.com.au to get a taste for Formula in NSW.

Windsurfer One Design is retro happening in the clubs these days also, if you are interested in super light wind racing with lot of others...
cheers