Finally!
I test drove the new E350 convertible Prime Edition the day it came to Vancouver, and I have to say - What a magnificent car!
Got it with 18 km's and returned with 34; not much for a descent test, but enough to get the rough idea, as I was already driving CLK 350 convertible for 3 years.
The engine and the gearbox are the same, so one can expect to make 14 lit/100 kms on daily commuting and occasional 5-600 km's freeway trip (that was my average from the last 36,000 km's).
The space is similar to the CLK, the ragtop is exactly the same. Can be opened/closed while driving also (not driving fast though).
I haven't purchased the one I've tested as it had some stuff I don't need (like GPS) and had a white seats (Prime Edition) which I don't like as I wear jeans often.
But, with its excellent list of standard equipment, and black leather seats, I couldn't find a better 4-seat convertible than E klasse.
Maybe a CLK, but that's now out of production
or BMW 6, but that's an old model soon to be replaced...