Thank you, jw, for your usefull information. I have downloaded the Jim Douglas calculator. I also sended the info to my instructor, but unless he or Starboard themselves convince me otherwise, I think I will prefer the Rio S.
I find it somewhat surprising actually that board manufacturers do not specify weight categories for beginner boards. Maybe some sort of size chart for beginners by Starboard would help them buy the right stuff.
Of course one can test boards by taking lessons for example, like we did. However in most surf schools they do not use the very latest boards (would be to expensive, I suppose). In the case of the Rio, its shape and sizes have changed substantially these last few years, so the board I surfed on, does not help me make my choice.
Thanks a lot!