The IC is indeed much more central but you are going to spend A LOT more money. Renting a car in Rome is the LAST thing I would do. It's crazy to drive there and parking is nil. I found the taxis fairly reasonable and like I said, the shuttle at the CP seemed very reasonable... it might have been free but I didn't check into it as I was going a different direction and a taxi was my only option. Not sure about their metro situation. As I said before the CP was a beautiful property.