First off, the oil from the factory is regular.
I didn't change mine until 6k, but it wouldn't hurt. The 3.6 is a very robust engine. I've been running regular oil since new with no problems, at 18k miles.
If you want to spend the extra cash for synthetic, go for it! It sure can't hurt... LOL!
Many change their oil well before the suggested 6k mark.
As for synthetic...IMO, most regular (read non-synthetic) oil is just fine. I stopped using synthetics years ago in my cars, trucks, bikes, and four-wheelers and I have vehicles that are nearly 15 years old...they have no oil-related issues at all.