Well if you do a Portsmouth conversion you will come up with a rating of around 44. From my experience if it is blowing over 6-8 TWS you will destroy this rating and under 6-8 TWS you will not be competitive as the keelboats have much better VMG in the lower wind range.

When our friends sailed their Tiger in a 15 mile round an island race in about 10-12 TWS they were about even with us on the 65 foot boat I run, which rates -69, until the wind shut off and we finished and they didn't.