A good article rather than an M3 comparison might be the E30 M3 against a late model Turbo 944, C4 Corvette, and maybe even a 328 for a true low end exotic benchmark. With the exception of the 328, these were very much in competition for buyers, with the M3 being the only true 4 seater. They're all in a similar price bracket today for good ones, and I assume, many of the same buyers might also be swayed one way or the other, as long as they aren't diehard BMW, Porsche, or GM people.