First, that was a very cool video! In regards to cold water-fast water, I've always thought of cold water as fast becuase yes, the denser, more buoyant water makes the ski ride higher on the water, just like a faster boat speed makes the ski ride higher up on the water. That's why 60 degree water can make it feel like you're skiing at 36mph instead of 34mph, and 90 degree water can make it feel like you're skiing at 32mph instead of 34mph.