Once you get comfortable with the boat which you should be by now after 10 sails... I would say up to 18knts would be okay. I have had my 5.2 out in 25 with a crew and believe me things are wild. Solo I do not go above 20.
Once you go cat you never go back!
Nacra 5.2 (Elsies)#1499, running an inter17 spin!