The Mustang is a pony car. GM's competitors for it were the Camaro and Firebird.

The GTO is a real four seat luxo/muscle coupe. The closest Ford equivalent to it is I guess the previous generation Thunderbird. It was a big rwd coupe with a V8, although I would surmise that the GTO sucks a whole lot less than the old T-Bird did.





Similar in concept, much better execution on the part of the GTO.