Thanks everyone for your experience and advise. In the end I decided to on a GORI 3 blade folding prop from AB Marine and after a season in service I am very happy with the additional speed under sail. Under power, the over drive feature is great getting around 6-6.2 knots @ 1500 RPM on my 72hp Mercedes Diesel.
Have emailed AB Marine on a couple of accassions to enquire about blade size but no response - perhaps an indicator for future service performance ?
All in all, very happy with my GORI prop.
Dan, Celestial 48'
Toronto, sailing Lake Ontario & Thousand Islands