195/45 is perfect on 15x7 imo. Anything smaller is just for scene points and it sounds like that's not what you'll be going for.
Plus, you'll need as much tyre area as you can get to allow all that power to get to the road.
On stock tyre size (175/70r13), my STD 1.8 8v was spinning the wheels in the first 3 gears. Just sayin