Hi andrew, the Stubby is obviously longer as it´s a real SUP board with foil boxes built in afterwards. So it is a great SUP, pretty good for both WS foiling and SUP foiling, although of course the modern foil board shapes are much shorter and easier to ride. As a Wingfoil board it´s ok, but pretty long, I would say that is the weakest discipline that it works for - but it does work.
The Sky SUP WS Edition is obviously built for SUP foiling and wingfoiling, so it works great for those, especially as an entry level Wingfoilboard. As a windsurfing foil board, it´s not bad, pretty nervous as it´s really short, so you need a bit more experience as a windsurfing foiler than you do with the stubby - on the other hand the SKY SUP is bigger in volume, so with a bit of pumping, it will get up and going quicker on the windsurf foil.
Purely for Wingfoiling, you can´t compare the 2, the Sky SUP is substantially better, hands down....and generally once you start wing foiling, you will be mainly doing that in the end on that board, so much fun. What do you weigh? done any foiling yet?