If your car is really slammed then I'd play it safe and get the 4-2-1. It doesn't seem like you have serious performance plans for the car and so I don't think the difference in performance potential between the 4-1 and 4-2-1 is large enough to be worth the risk of scraping. There's only so much you can do with the stock collector size anyway, if you wanted to make high power you'd be looking at something with big primaries and a 2.5" collector and then you'd definately scrape the hell out of it.