I have an '06 Cayenne S and an '05 RR HSE (not a SC). They are completely different vehicles to be sure. The RR is more truckish, while the Porsche behaves like a sports sedan. In Brazil, I doubt you'll be too concerned with snow/ice handling, where the Porsche with snow tires dominates the RR. The SC RR comes with 20" wheels, which you can't easily get fitted with snow tires. 19" wheels will fit over the Brembos, but finding either true winter or off-road tires isn't easy. I bet, depending on the driver, a Cayenne S would do just as well off road as the RR.
I had, and asked, the same question as you when it was time to buy an SUV. My buddies said, "Range Rover, no doubt." So I did (I had had my heart set on the Porsche until the Land Rover dealer made an offer that brought the price down into my league). Then my wife bought the Cayenne S!
Now I prefer driving the RR. It's feels bigger (though you should check the exterior dimensions of both... I believe the Cayenne is actually wider.)
If it's a toss up, go with the best dealership. They're both great vehicles. My vote is RR, though.