Thanks for that. The size they recommended just seemed to contradict the Mistral school in Roses so a 3rd opinion most welcome. Chinook is where I have the demo kit from. I have bought kitesurfing gear from them and they don't seem to be the sort of outfit that would 'fob' you off with an unsuitable setup. Forecast is good for tomorrow morning so will hopefully give it a go. I have had a go on the Teleski, can't remember seeing many windsurfers but will drive up there for a look. Shallow water sounds good.
Also have the Barrage D'Agly up near where we live, probably pretty gusty and you have to keep your eye out for water bombers charging down the axis (or so the sign says) but once I get a bit more experience it could be manageable.