yeah, so a 12cm exh. housing will spool faster than a 14, but will have higher egt's, and more drive pressure, cuz it is more restrictive for the exhaust to get out. it's all a toss up, you have to scrifice somewhere. but with the setup you're looking at, you need some serious egt controll. i hit 1600* with my 150's and adr real quick. i'm actually gonna get a 64 on mine. but if you go bigger you get more lag. and more smoke tryin to spool it