depends dude if u stay on styock turbo i would upgrade to like a ghl 2.5 would sound great and effective but if u are going big turbo i would wait and put a 3 inch ounce ur big turbo is on
i wouldn't touch GHL personally. some guy on vortex cut apart a 3" GHL exhaust only to find that it was in reality a 2.5" pipe with a 3" sleeve on it. now i don't know if they are doing the same thing for the 2.5" exhausts but as soon as a company does something like that i would stay away personally.
I have a 3" DP and a Neuspeed 2.75" catback (2.75" magnaflow high-flow cat) I like the sound because it's not outrageously loud and very effective with my set-up.
2.5 GHL TB, no double layers on mine. Sounds great lil issue with the rumbling on the center console but only on cold engine settles after that, pefect for stock turbo though