If the Cobra guy is a top notch driver he will win all day. The STi can hit low 13's all day but breaking into the 12's stock is very very tough. A 12.7 was run once and once only on a stock STi and I have no idea how that happened. In a drag race it can go either way depending on the driver, but I think the Cobra has the advantage in the end.
But if you are going to be doing a roll race, the cobra should win all of the time. However if you are going from a stop on the street, STi will be able to hook up a lot easier and get a nice lead on the Cobra, so that race could be won by the STi, due to the AWD advantage on launches