With a wing of that size, I think it looks off if that's all you have on your car. Though if you did have other body pieces (like a rear valence, sides, etc.) then it'd probably look more proportionate.

But since the wing is black on that car, you might be able to get away with it (kinda like the 'black looks slimming' idea). But to me, just having a wing that's bigger than normal just doesn't look right on an otherwise stock car.