In my GT i have a 18 bell and a 62 spur gear and that is far more than enough ,any smal stone on the track can launch the car up in the air ,i have tried a 20 t bell but the MIP clutch burned with it and i now have a alloy home made clutch that will never slip .
Believe me ,a 18/62 combo will get you to speeds that might scare you with a GT