Nope no experience with whitewater on a sup. But here are a lot of German people for the windsurfing during summer. Those people would love to show and talk about they're equipment so that's how I know about this. I only have a hardboard windsup, a hybrid for flat water and catching the waves. One collision with a stone and the board is broken (had it already 2 times...)
RE: Top 10 SUP Safety Tips Guide