07 sti vs 08 mustang gt?
Look at the important things... You're car is AWD if I'm correct (bmw guy), and much lighter. He's driving a rwd titanic. My cousin rented a mustang gt, and was sorely disappointed. You should take the lead right off the line, then it'll probably come down to driver skill. He's got more HP and Torque. By the way, the cold air intakes and exhaust typically add horsepower at the redline, and right before it. To complement those upgrades, look to upgrade your chip. By changing the stock chips configurations, the extra air flow created by your upgrades will greatly affect the lower and mid range RPMs. The guys at Speed Tuning USA flashed my chip for me. I had a K&N intake that added 9 hp at 5800. With their chip, they pushed my car up from 190 hp and 207 ft lbs of torque, up to 217hp and 230 ft lbs. It most noticeably affected the mid range, which is where most cars lag.
Hope that helps, I hate mustangs.