Spot on... it comes down to each girl's own "sphere". If all her friends' boyfriends are just driving civics, a regular 330i will do wonder. But if all of them are driving lambo's then you look bad driving an E class.
Think about it this way... if all your close guy friends' have ugly girlfriends, then a solid 5 will make you look great; but if they all have solid 8+ then you might feel like you aren't as good as them.