The CT won't give you any more cabin space than your sedan. I really like the M5 touring and RS6. I'm making the assumption that the M5 touring will have better performance and technology than the RS6.
It's inevitable that you'll accumulate rock chips. You can always try Dr. ColorChip to cover up the chips. I wrapped my front end with PPF so I could keep my OCD at bay.
I could live without the pano roof. Would prefer steel or carbon roof. I've lived without ambient lighting and it makes a difference. The interior just feels so dark at night.