yeah, the 255/40-18 will be too tall. Try the 255/35-18 size. This size will be a little shorter than the 265/35-18 but will give you better steering feel and will allow you to accelerate out of the corner slightly faster. They will probably also be a little lighter than the 265 (same tire model).
Another route is to go with 17" wheels. 17x9" and 255/40-17 tires.
Or go to even lighter stock sized wheels at 17x8" and 235/45-17 tires that are really really sticky! This will give you the best steering feel too.