As to gear selection for your Turbo car, rule of thumb is more gear is bad for a turbo. A turbo needs load or stress to allow the turbo to spool. It's not just rpm, as many think, it is load and exhaust flow.
What is the rear gear that is in it now? I would drive it and see how it feels first. A turbo is not a supercharger, it doesn't need rpm to make boost, just load, which increases exhaust flow.
Max I would recommend would be a 3.55, and then that may be too much. When the turbo spools, torque goes through the roof and a 3.55 may multiply that torque and blow the tires off, where a 3.27 may be tamer on the street.
Sorry, just trying to help. I have 2 turbo cars and have built and tune a lot of turbos.