We are running a C4 which only has 3 gears. We, like you were only using 2 gears. Our 3rd gear was perfect. We would hit our red line, which was 5,000 rpm's just at the end of the straight but man was it a dog going from 2nd to 3rd.
Yeah the wing makes a huge difference. Turn 3 at t-hill was awesome. We could stand on the throttle on the outside and just fly by people. Everyone on the team had a story about how they got crossed up and the wing "saved" them. With the exception of one of our drivers losing a wheel and spinning we never had any driver spin the car.
We are going to try to experiment with some type of springs under the rear wing mounts so that the faster you go the flatter the wing gets. So far we are thinking about valve springs stacked on each other inside of a telescoping rear wing stand. This will require many trips up and down our road though to perfect!
E=MC Hammered
E30, 302I (ME car)
Pintoghini with turbo 2.3L
Old Spice Crown Victoria