Has kevs says, depends on your roads and where you want the power to come in. Where i am GT30 works a treat, theres no lag but it runs out power where the GT35 keeps going. Im running GT30 with SP 263s , SP intake ,SP chargecooler, spacerplate, ARP bolts. 400bhp /380lbft at 1 bar this set up would piss over mate RS