If your going NA then for sure the more torque engine, B20, would be the nicest option. But if you want to beat that ITR, consider saving and doing FI. Get your 300 hp easily out of any B series motor. The B16 will be your best bang for the buck and a more reliable option if FI, although GSR is probably better but more $. How much is a B20 anyways? what is your budget? what are your expectations?