I had a Quaife diff fitted to my last W212 E63 without any other work being done at the same time, so pre / post comparison was not diluted by a "was it this or that that caused the difference" question.
What I noticed fairly quickly was that the car was actually quicker accelerating even in a straight line in dry conditions. I put this down to the traction control silently intervening to minimise wheelspin on the open diff, and the rate of rear brake pad wear on that car tended to support that diagnosis.
Have fun