Well, the (supposed) benefits of a roof tent are that you don't have to make/undo the bed when setting up, but that it folds along with the tent and doesn't cost time.
Sleeping in the car is less windy I would guess. Did you make blinds for yours? I slept in a V70 once without blinds and woke up really early!
I did see a YouTube video of a guy who car camped with his V70, is this you







