Great day (beggars can't be choosers).  I put in my new Select S12 47cm, which I got for another board, rather than my usual S10 53cm.  The sail is 7.5m2 and this board is wide at the back (and 100cm wide).  The 47cm was a lot more fun, in gibes and manoeuvrability.  Excellent fin, I worked it hard and it didn't spin-out once.  In the end it was not quite a quick in top-end speed as the 53cm because I couldn't ride the fin as much.  I did manage 52kph though. The biggest difference is it could go further through the gybe than the 53cm.