At the NMCA finals in Memphis a few years ago, I messed up on a qualifying run and ruined the favorable index I had already established. (they lower your best et by .1 and that is your index)

Since the car wasn't fast enough to run the new index, we stripped it. Pulled the bumpers, tail light assemblies, carpet, door panels, wheelie bars, AND the rear wing. At almost 150 mph the Duster behaved exactly the same with or without the wing.

My wing is not that large, and Dusters have a pretty big decklid area so maybe that is why it didn't care about the change. I'm sure the body style has a huge effect on downtrack stability, maybe a bigger effect than the wing itself.