Stewart,
Problem is ISAF SCHRS is a paper-based rating system with a mathematical formula which swims upstream against common logic.
I punched the following numbers into their spreadsheet just for fun :
A 16ft boat with a 25m mast, 75sqm mainsail, 25sqm jib, 100sqm spinnaker. Weight of boat is 25kg.
The rating it spits out is 0.44, more than twice as fast as a Tornado.
Anybody care to take this boat out for a sail in anything more than 3 knots ? Of course logic tells you this boat would not be feasible, ISAF says it would just be helluva fast.
IF it could be sailed, that is !

Other rating systems which are based on real performance data collected over time are probably more realistic, the Aussie system looks like it works this way. Some boats are fast in light breeze,
others in stronger wind, some like choppy water more than others. No numbers based system will issue absolutely fair ratings, or even sensible ones IMO. Issues such as hull shape & fullness, rocker, bouyancy etc
all have a marked effect on making one 16ft boat sail completely differently to another, yet ISAF`s system only looks at overall length & waterline length. Their system isn`t bad, it just can`t possibly cover all the variables
in different designs.
You`ll find that once F16 regattas actually start to happen on a truly open-class basis ie Taipans, Stealths, Bimare`s, etc on one racecourse, one boat will shine through as the fastest, even although the ratings are all the same.
It may happen that one boat excels in light wind and not in the rough. Only practical comparisons will tell.

Aah yes, and then there`s the question of the nut on the tiller.

Just go racing, have fun & don`t let anyone finish in front of you. Handicap, Shmandicap.

Cheers
Steve