I'm pretty sure you're right about the Camaro being more economical than the GTO with the A4. But I'm pretty sure the M6 versions are going to be about equal with the new standards. 16-23 right? The M6 GTO was rated at 17-25 under the old standards.
And did anyone else notice that with CAFE standards rising to 35mpg, we also have to deal with a less generous rating system? All of a sudden the EPA changes their testing procedure to make it harder to achieve.