To be honest you would be better off with the BBR Super 220 conversion of the 2.0 ND2 rather than a turbocharger. The conversion produces 220 bhp at 7,800 rpm whilst maintaining a very flat torque curve. The increase in torque over the standard engine is only small which in the ND MX5 is a good thing as the ND gearbox has a limit to how much torque it can withstand. For turbo conversions BBR recommend fitting the NC gearbox using an adapter. However having said that I do not know the torque capabilities of the automatic gearbox on the ND.
Got to say though, after having the BBR Super 220 conversion done to my ND2 (soft top) the engine is a wonderful naturally aspirated experience all the way up to the rev limiter. According to a BBR YouTube video the Supper 220 is capable of 0 to 60 mph in 5.4 secs which is plenty fast enough.