MP,
The SL500 is actually several hundred lbs heavier than the 500E and for the years that both it and the 500E existed in the linup the SL500 had taller gearing. (2.65 for the SL and 2.82 for the 500E) Don't get me wrong, the SL500 still is a quick machine, but it is no 500E. The combo of more weight (3800lbs for the 500E vs 4200lbs for the SL500), slightly less power, and taller gearing all hurt the SL500's performance vs the 500E. I know the 500E's CD was 0.32 but I don't have that spec on the SL500 in front of me. I'd imagine that it would be worse so no advantage there. If you want something to cruise in, get the SL500 as it will give you good performance with some pomp/prestige. It also has the upside of being a convertible. The 500E is more suited to being able to take out a corvette but looking very low key (stealth). (think hit-man in an armani suit)

Handling will also go to the 500E as all the Sl's I've ever driven feel very disconnected and heavy. The 500E's feel much more direct and precise. Guess that is the 400+lbs less weight and Porsche suspension making itself known. You could say the 500E is "part 300E, part 500SL, and part Porsche" Drive both cars and see which one appeals to you the most. That will give you the answer more than any spec or table. Whichever one pastes the biggest grin on your face the longest wins...

Hope this helps...Lee