I'm a bit partial to the Audi, I know it wasn't mentioned by the OP though. I'd still have to lean to the XM vs the Turbo S. My wife wants to trade the '08 Tahoe for the Audi also so that may happen sooner than later. I will have her check out the XM again though too.
2001 BMW 525i
2008 Tahoe LT
2004 Silverado SS 370 H/C/I N2O FLT lvl5 4L65E