I meant to say "grip limited". The Mazda2 is fairly anemic, and I feel that 195mm wide tires (of summer variety) are more than sufficient for corning grip. There is a definite trade off when you're trying to fit a wide tire on a narrow rim, and my background Miata experience has proven that 205mm goes on a 8" wheel, and 225mm wide goes on a 9" wheel. I've run 225s on a 7" wheel, and it's rough because I'm not using the surface area of the tire in its entirety (ha).
I'll definitely post a trip report when I take the 2 on track over Easter weekend, but I think that 195/50R15s + a rear bar is going to be the sweet spot for the weekend warrior types who drive a Mazda2. The wheel/tire combo can be H Stock or STF legal without a huge weight penalty or fuel economy hit, and the car will still be plenty tossable and fun to drive.