Sorry Roger, I wrote "ALMOST everybody" to be able to exclude you, as I know you have lots of experience of boards with daggers.
It is quite possible that the Rio M offers the same speed as a P320 and a Kona One (which is my board) in 20 knots of wind. I don't see any reason it would not. And I have the same experience as you do, shortboard freeriders need to be pretty good to overtake me on my Kona!
And I do believe that the RIO is an excellent beginners board. And you can take it out in planing conditions.
My point was that I believe it falls well short of a P320 for regular use on a lake in non-planing conditions. There the P320 can benefit from longer waterline, glide, a big and effective centerboard that promotes railing when going upwind.
I feel that the Rio is an excellent stepping stone for shortboard windsurfing, but it is not the end game in the way a P320 can be in a lightwind location.