Know what you mean to much noise is annoying for your Mrs when she's in the car but medium sounds are fine, Iv'e got MillTek Non Res catback on mine sounds great.
WOW! Lots of power then, my Scooby only has the stock engine which produces about 262BHP, but has a Milltek Non Res Catback Exhaust it's loud. The 600BHP could be quicker than a Nismo Skyline GTR R34?