2 questions, first, i have been advised that tire/rim weight is a huge impact on the overall weight of the car, just want to verify this, and are stock rims (eg) the lightest or are aftermarket ones better?

second question, my car is somewhat lowered, there is still about a 1" gap between the tire and the body, i am wondering what would offer better performance: making it lower with stock size (195) or keeping it at current height and using wider (205-215) tires? btw, i currently have 00 si rims.