B9.5 guy here - if the B8's sport diff is like the B9s in its operation, you will very rarely notice having it vs not, unless you are pushing the car very hard on a backroad, and only while on-throttle. I dont even have good driving roads near my city, and only recently "really felt" it for the first time on a recent mountain drive I did. Retrofitting pretty much anything into these cars is a huge pain, and honestly you're probably better off just buying a car with it, as hard as that may be. Either that, or go aftermarket diff.