We are all a bit off target if that's what you mean, the original question was "y would someone put a supercharger on a supra? also y would someone only have a single turbo?", and it has been answered.
Why are you still complaining about lag? Were talking about 2-3 seconds at the most with a big turbo waiting on full boost, then between shifts there is no lag for the most part so why do you see it as such a problem? IMO a turbocharger is much better for the streets, the setup is perfect if it makes all it's power over 3500rpm, ontop of that the power comes on and grows smoothly unlike a roots blower where it basicly just hits then dies off. If your driving in the rain you don't want 500hp when you barely push the throttle at low RPM's, where you could accidentally blip the throttle and wrap the car around a tree. Why wouldn't you need all the power at high RPM for the streets anyway, for daily driving you don't need more than 150hp to move the car along with traffic. I don't know about you but how often do you go around flooring it between stoplights like the soccer mom in the minivan beside you, where you require 500hp to get to 45mph. Whatever the case is the simple fact is that the turbocharger will always beat a supercharger, in versitility, in efficiency, in cost, almost every way possible. Good luck with competitivly racing the 1jz, got any pics of it by the way?