think HKS hiper is the best bang for your buck. i have a GReddy PE on my NA, kinda loud, but no complaints really since it's a performance exhaust, that's what i expect. you can also hold out for info on GReddy SP2 exhaust that's supposed to be coming out, they quit making GReddy SP's. i'm sure others will chime right in with B&B Tri-flow and "Get Labree" but i don't know specs on those really...