Again Norbie preempts me (btw I hear you got a letter in the mail?)... prettymuch spot on.
Outright straight line you might go okay against a stock auto turbo.. but you'd really have to give the atmo one hell. The low-down torque from the turbo motor will give you heaps more at part and mid throttle - you're right, it will transform the car.
And once you do somethign as simple as stick a good exhaust on a turbo one... you'll walk all over a modified atmo one.