Actually, thats the opposite. In the teaser we were sailing upwind, and
there aint no potter gonna make progress against a 6knot current :) I truly
doubt potters can make good faster than the wind speed for a dead downwind
destination. Some high performance boats can (Melges 24, most any
boardsailor) comes to mind, but not a potter.
This teaser question lived on a lot longer than I thought it would. my 2
cents is that the boat where the current and wind are the same will go 2
knots no matter what. Sailing is based on the wind and water going (at least
slightly) different velocities. If it isn't, the boat can't get started, and
even if it could, the apparent wind would always be dead ahead and you'd
always be in irons. Its the exact same situation as still current and still
wind - and we all know you just sit there - its an inertial frame of
reference, and all the laws of physics and relativity still apply :)
The other boat (assuming a weatherly rig and enough sail area to take
advantage of 2knots) should be able to make some VMG against his apprent 2
kn wind opposing the current, and should win the race.