Originally Posted by Red Bread
The SL is a two seater, with a cosmetic back seat available in some markets. The 6er at least offers the pretense of a functional backseat. I have yet to see a four seat hard top convertible that doesn't look silly, the E93 being perhaps the worst offender, so I wouldn't trust BMW to do this right. Of course Ferrari even screwed up the California, and it's got about as much interior space as the SL.
The SL is significantly smaller and less grand tourer. The 6 is more competitive with the CL or upcoming S coupe. (although really the 6 lands somewhere in between the 2).
The hard top would look silly, weigh an extra 300lbs, and be far less elegant with the top down.