I have an APEXi GT-Spec.. It's fully stainless steel unlike the N1, and it has an inline resonator...
When it was just the cat-back it was extremely quiet... Now that I've put the rest of the exhaust on (HKS dumps, HKS front pipes, 3" cat) it's gotten a lot louder, but still not too bad.
It's also a 95mm (3.74") which is as large as you'll find in japanese exhausts. There are no such things as Trust 4" exhausts, not in their current lineup at least. Their largest exhaust is the on Ronin 09 has (the TR Power Evolution II) which has 94mm (3.70")... But that exhaust sounds like a fricken CANNON
If you have an unlimited budget, I'd definitely suggest grabbing a Fujitsubo Super Ti
http://www.fujitsubo.co.jp/mc-prod/psrs-v....hp3?id=00000075
Full titanium cat-back exhaust, soooooooooo light, and sounds absolutely HORNY
Here's a sound clip of it on an R34 GTR (P.S. On the Fujitsubo site, they have sound clips of all their exhausts)
http://www.fujitsubo.co.jp/imglib/sdra/sc_vol5/12.rm