When you are getting the lift on backside of the sail -- or what I enjoy saying "doing the Bernoulli (Brr-NEW-lee)" because it sounds Italiano -- you certainly are going to get the speed.

The "telltales were stalling" because the sidestays do kill the shape, but the shape has more to do with lift and there is no Bernoulli when going downwind.

On the Wave, I don't know of anything to make you go faster downwind except installing the traveler or doing the broad reach. Which sounds like you did.