Single = not near enough flow. RL, dosen't the stock GN turbo only flow enough air to make about 400HP?
For twins, you dont have enough cubes to spool them quickly. Unless you are going to build a 427 stroker, or some spray to get them started, but for the street, why? If you are putting that kind of money into an engine, get a set of turbos that actually have a compressor map that matches your motor.