Sorry for this post as I know it's a bit late and the thread has changed a bit. Last July Bunt and Factor were asking about experiences upwind on the L39. I finally remembered to take a picture of our instruments this past weekend. I'm not yet a very good sailor, so I think with the correct sail trim this could be improved, but this is what we were able to maintain, up to about 5.3 knots for about 3-4 hours up Colvos Passage in Puget Sound.
you should mention sea state as well as many on CF will compare your results to their flat water ideal conditions performance.