vortec superchargers have a much better design, If the charger is geared correctly, it will make more boost faster than any other charger. I have a friend that makes 14lbs of boost at 2200 rpms and it only builds from there, redline at 8700 it makes 26lbs...uber fast... more torque that a sti out of a corner, fun stuff...
They have a different design, which is not inherently better. Sure you can get cooler IAT's, but with an intercooler so can the positive displacment blowers. And, by design a positive displacement blower makes boost instantly. No building, it's there all the time. To get a centrifugal to make boost down low, as you suggest, you rev the snot out of it, and like you point out it makes 26lbs up top then. You can get 10psi on the low end with a positive displacement, without having to run 25+ on top. Centrifugal chargers cannot by design make boost faster than a positive displacement charger, same way a positive displacement charger by design will never be as efficient as a centrifgual charger or a turbo.
For a d-series? Turbo all the way!
