you can run decent into the 12's with your setup, and im guessing the m3 with the dinan exhaust can get no better than 13.0, and thats if hes lucky. if your on the street you own him off a dig. from a roll he will slowly walk you a car or two, and the faster you go the more he walks. i assume your using a DTS dyno or the like. also i would imagine the bmw might also be chipped and just not telling you. i wouldnt lay any money down on this one.
...oh and good luck