For shit sakes - there's nothing wrong with keeping it like it is. 3er, 4er, 5er, 6er, 7er and - for entering the dick-measuring contest with the Merc S-Class Coupe - an 8er would be just fine.
I'm hearing talk that the 5er GT (which is like a big 3er GT) is going to become a 6er, and the 6er is going to become a - aww fukkit - I've got better things to occupy my time with.
I'm beginning to think the product planning and marketing teams aren't talking to each other anymore, and both basically use a set of dice to come up with everything.