Erin- The Rio probably planes a knot or two earlier than the Kona because it's wider. But based on my experience riding wide hybrid boards like the Mistral Prodigy, which is similar in shape to the Rio, I think the narrower Kona is smoother and more comfortable both in gusty wind and in really strong wind. But I guess you have to use what will fit in your car.
The max width for raceboards is 70 cm, and the max length is 380 cm. The best board to win in the raceboard class would be a true 380 cm long raceboard like the Phantom 380 or Mistral Superlight II, but a slightly shorter longboard like the 70 x 350 cm Kona can do OK in those races. A wide hybrid like the Rio will be at a disadvantage unless the wind is strong enough to be fully planing around the course.
Good luck with your choice.
PS- That isn't me in the video- it's a friend from Canada. But I do windsurf in the winter here in Virginia, where it's usually 7-15 degrees C.