I'm a huge fan of the B20 engine, but in this case I'd have to go with the GSR engine. Sure you get more torque with the B20, but like the other answer said, it has to be built up before you do anything to it. You'll have to build the GSR engine to get over 7 psi of boost too but you are already steps ahead in your build if you choose the GSR engine over the B20. BTW turbo it,then maybe consider NOS later. You do want reliabilty don't you?