The main reason to upgrade a clutch is to keep the clutch from slipping under high torque. If your car is stock, you should not be having any slipping problems. Therefore you would be better off stock and saving money as well as avoiding any negative drivabilty effects. If you were to start running high boost or somehow make high HP with naturally aspiration you would notice the stock clutch will not hold up and will not grip properly. Actually right this moment I am half way done installing a new SPEC stage 3 clutch over my stock one because i'm now boosting 12psi and my stock clutch is not holding the power. I virtually do not have a 1st or 2nd gear at full throttle, the clutch just spins, RPMS soar and the car doesnt go anywhere until I hit 3rd gear.