I finally got out with the junk rig again. I'd cut off the Gurney flap because I just couldn't see it being a benefit on a fast easily driven hull. Maybe the high lift/high drag device would be of benefit to a slower heavier hull. In any case I did max out at 10.2 knots of boat speed in a 10-15 knot wind.
I even reefed on the way home just to see if it is as easy as advertised, and it is. I eased the sheet, went forward and lowered the sail down two battens and it was done. The upper sections of the sail are cut flatter than the lower sections, so you are all set for whatever the wind gods throw at you.
There is one detail that you don't want to forget when sailing any small craft. Be sure that there is some way to prevent the mast from coming out of its step in the event of a capsize. A partial dislodging of the mast can cause all kinds of damage to the mast collar, the hull or to the mast itself. In the photo above I have hose-clamped a section of bamboo around the mast just below the deck and collar. A down haul line from the boom to the deck will also do the job. I have done mine this way to allow the mast to still rotate.