You can get a nice 2.5" custom exhaust for around $300. For the size of the motor and the boost level I would not go less than 2.5". When I moved my exhaust on my 2.7l supercharged motor from 2.25" to 2.5" I went from a 103mph trap speed to a 105mph trap speed. It made a really nice difference and would make an even bigger difference on the srt6. You could always get an electric cutout installed and leave it closed or only partially open on the street and open on the track if you want to keep it quiet on the highway.