It's fine to go for the larger XL size if you need the longer loading surface. The Sport has a loading surface of 130cm and the XL had a loading surface of 160cm. The larger XL won't look quite as neat on the vehicle so most people do stick to the recommended size. You can fit a lot of gear onto 130cm bars, especially if you top-and-tail your bikes.
Your load shouldn't stick out further than the widest point of the vehicle (excluding the wing-mirrors), but most estate and hatchbacks are 180cm + in width, so this shouldn't be an issue.
Here's the XL size on an Audi A4 estate: