Recently got the Fujitsubo Super Legalis R on my r33 gts25t, personally i stilll think its too loud compared to stock, hey Razorsharp, need to meet up with you some time to compare, i know on idle the Fujitsubo is loudish, i haven't revved my car yet because still braking in the engine so can't tell you what it sounds like on full throttle.
i use to have an Apexi N1 and it was VERY LOUD, ahahh too loud for my liking, but i've got high flow cat and custom front pipe and alot of other mods (forged pistons, high flow head etc etc) that could affect the noise level as well, BUT personally i'll prefer the Trust PE2, from experience on a s15 and other ppl's opinion everyone said its nice and quiet.
my 2 cents