In short, backpressure in the exhaust is a heaping pile of bullshit.
If you're running the car on the street, put a REAL exhaust system on it that meets the legal requirements to be insured and tagged in your area.
If I heard a MkIII Supra rip out my ear drums just by accellerating from a stop light, I would go home and sell mine in order to avoid being associated with that douchebaggery. Is it really neccessary to make that much noise to get to 20km/hr? I've seen (heard) civics, tiberons, neons, sunfires, and alot of other rice, that are louder at idle than my 7M is at WOT... wtf? Get a real muffler assmunch.
Let me translate the sound of a fartcan/lack of muffler, pulling away at a stop light, for you:
IIIIIIIIIIIIIIIMMMMMMMMMMMMMMGGGGAAAAAAAAAAAAYYYYYYYYYYYYYYYYYYYYY
If it's a track only car, by all means bang away without any exhaust. If you're going to street it, do us all a favour and get a real exhaust system.
/rant