A Miata with:

Koni Yellow
GC coilovers
FM sways
FM rear shock mounts
assorted braces

Will be sick y0.

Granted on a large road course with lots of straits the horsepower of a nicely set up RX-7 will own the crap out of a Miata. But on an autocross course the FD is a little tricky and I haven't driven an FC so I can't really comment. The FD is a great car for circuit racing but in the really tight spots I think the Miata has it.