I was in this boat just a month ago. I chose E70 4.8i because I don't need off-road capabilities of a Cayenne, plus, if you equip an X5 and a Cayenne to similar option specs, for the price of base 3.6l Cayenne you will be able to get a 4.8i X5. Add the 0.9% offer on top of that and it becomes a no-brainer.