I'd still suggest disabling .vp's one by one and seeing what the result is. If nothing else, despite everyone writing it off as a driver issue, you could see whether any of the assets are causing lag.
Edit: And the reason I say that is because I've also had the game not very happy with rolling the ship on a GTX375, I believe there may be issues with the way FS2 handles some resource, and, as most of the coders will tell you, it's not just about raw GPU power, it's also about how the assets are accessed and manipulated.
Maybe there are some problems with OpenGL on newer drivers, but it's probably better to do it by the numbers than just assume that.