Depends on where you are racing. I've beaten/beat Mustangs at every single autocross i attend. I even beat them when i ran my Zx3 on the FRPP suspension. Last season when i ran my SVT out at Miller Motorsports Park (road track) i beat two Mustang GT's, not by much, but i finished ahead of them. i doubt my zx3 (2.0) could hang with them on the road course.
here is an easy solution, get a Miata and you will show him what's up! ZOOM ZOOM!