When I had the EFR turbo, 91 octane at 4700 ft elevation, 320 WHP, 287 ft lbs, lag then hit hard in the mid 4k RPM range, LSD, 225 Rival S tires on 15x9 wheels, suspension bushings, coilovers, above 60 degrees out, 1st gear was hard to use but no wheel spin at all in second gear on decent roads but lots of torque steer to deal with and a great deal of acceleration fun. The right mix of parts can yield great traction when running lots of power per weight, my car was 2575lbs then, 1st gear could of used some tuning to limit the wheel spin making it more useful but I am not into drag racing, street or track so it was not an issue worth bothering with for my particular setup and use of the car.
The C39 is going to make your car much faster than most are expecting in far more situations than a Donkey kick stock turbo or a lag prone bigger turbo, I am very glad for all involved to be able to get one of these as a damn fine performance upgrade for the money, the best by far and more so that get to run E30, Meth, etc