People who assert that Cayennes handle like boats and are useless off road have never driven a Cayenne.
I took the 1st test drive of the Cayenne S the morning the car has been released in the US. I drove to the dealer in my 993. While the Cayenne is no 993, it's by no means "a boat". I test drove nearly every luxury SUV throughout that period and the Cayenne handled more like a car than all of the other SUVs out there. There are cars that could be envious of handling that well. The main reason we bought an MDX rather than the Cayenne was that we wanted/needed three rows.
And as for claims of being "useless" off road. seemingly this person NEVER saw the promotional videos from Porsche nor did they see the "off the road" test performed by the guys on "Top Gear", the British car afficionado car demonstrate that test drives Ferraris, Porsches, Lotuses, Jaguars, Lambos, .
The Porsche Cayenne Turbo and the Porsche Cayenne Turbo S are ludicrously powerful cars. zero 60 in 4.8sec? There are sports cars, roadsters, and heck, past exotics that can not pull that off. My 993 can not do that.
The G 55 AMG does zero 60 in 5.6sec? Heck that is faster than any CAR let alone SUV needs to be.
Personnally, I'd go Porsche. I have friends with an SL 55 and an SL 55 AMG. Beautiful cars. In the shop a pretty bit although. My Carrera is dependable though some cosmetic parts on the interior have broken easily .
But gotta I like the retro look of the G 55 AMG too.
Hey it is your money . or your dreams. Dream big. Dream big.

