It really depends if you are keeping your 535 or have another 4 door. If it was my choice and this is my daily or only 4 door, I would go with the GC. The GC has the combination of both M5 and M6, carrying the aesthetics of the M6 and the functionality of the M5. Also what others mention, the GC has folding rear seats and the M6 doesn't and you have the exclusivity factor. The folding seats come in handy for extra trunk space as you cant really put much on the M6 coupe rear seats. Plus you were already looking at a CLS which is a 4 door. If you are keeping the 535 or have another 4 door go with the coupe. Two door is obviously sportier than a 4 door. You have already made a good decision already by not going with the CLS
, now just weighing out the 2 door vs 4 door.