I have a SLK320 and I'm 6'4" tall, and I fit comfortably. In fact, it's one of the main reasons I chose this car over other roadsters from BMW, Porsche, and Audi.
The SLK is reported to offer Mercedes' best quality. I have about 6K miles on it without a single problem. I've heard there are lots of quality issues with the CLK. The back seat is basically a comforatable seat for small packages. The rear window is almost worthless because it's so small.
If want to stick with Mercedes, maybe you should wait for the new '04 SLK.
2000 Lexus RX300