Would you believe I just got new tires before even thinking of this
I think going past a 1" lowering is starting to get into areas where hot-rodders start counting the cost, so if you do that (2" smaller diameter) I'm guessing a 15% taller gear. If you are lucky, there exists a car model with plenty of cast-off wheels in that size (not always easy if you are starting with an eco-friendly car).