Why the magic number of 20psi? Only reason I ask is because 20psi on a t3/t4 is over 300whp at least. That amount of power is very controllable in a FWD road course car....unless you've got a killer suspension and an LSD equipped transmission. If you're looking to road course the car, a smaller turbo is prolly going to be better suited to you. You'll get better responsiveness and less lag, but the trade off will be less power potential.