If I am not mistaken, bernouli's principle states that as flows across a wing, lift is generated based on the fact that as air flows over the top, it has to flow faster which makes the psi go down and creates lift. That being said, the speed of the air at the rear of the wing should equal the speed at the front of the wing. I think that any difference in speed is going to be from inertia of the air over the top which is based on the mass of the air which should be pretty damn small. As long as the venturi nozzle is about 12 - 24 inches away and is free flowing, you won't get a significant back pressure. If you need help with the design let me know and I will see what I can whip up.

Travin