As much as I like the Cayenne (yes, I said it), I'd go for the V10 T-reg.
I know a couple who have one and they are totally in love with it. Also, they took it to a VW R32 meet at Tail of the Dragon and kept up with the R's, excepting the turbo and SC'd ones. Not too bad
I've heard that a nice upgrade for the Touareg is to install the swaybars from a Cayenne, and you can change the air suspension settings via Vag-Com to drop it a little lower at its lowest setting.
I'm in the process of convincing my Dad to get one to replace his Aviator when the time comes. It would make a great tow vehicle.