Don't understand why stability control for the trailer would make any difference to the performance when driving. If you are activating the trailer stability control you would have excessive sway. I have towed a fair bit with both an X5 and an X3, and the trailer stability control has never activated, even in snow.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue