My M3 can keep up with a stock STi on a dry road. My M3 has a better power/weight ratio than the STi. In a drag race the 390hp Cobra will wreck my M3, though. Humility is a good quality to have.
The STi is nice, sure, but 390hp cannot be taken for granted. The AWD and only 300hp in the STi catch up with it quickly and really slow it down.
OTOH, I've seen video of a *modified* STi run a 8sec 1/4mile.
-Daver