This has been on my mind for a while...

My girlfriend has a 2013 X5 M. Last time we were out playing with our cars, the results did not go my way. After about 25 or 30, mine is faster. The 0-30 part is the problem. I do not understand how I am getting beaten by this 5300 pound station wagon, which only has 100 HP more than I do.

Does anyone have good suggestions to overcome this problem? Are there any things that cause the RS6 to slow down with age? What should I check? Any suggested modifIcation?

Turbos are hitting proper boost, one intercooler is visibly leaking somewhat. I am replacing both with the Wagner unit in a month or so when I do my timing job. Thinking about electronic remapping, either APR or custom tune by a local Audi shop that my friends love. What else might put my sport sedan ahead of her station wagon?