Today I got the newest rumor regarding the future of the supercharged x55 engines. Apparently DC really wants to abandon the supercharger and go for a twin-turbo charged V8 engine instead. There were thoughts to offer a 6.0 V12 on the current E55/S55/SL55/CL55 models but apparently it would increase production cost. Giving the fact that the facelifted C-class and the new SLK get a normally aspirated V8 engine, the logical conclusion is to offer a bi-turbo charged version of that engine.
I heard this rumor before and I think I posted it in an older post but I never really believed it.

So I really think there is a good chance we see a bi-turbo charged V8 4-valve engine on the facelifted E55/SL55 by 2005, power is rumored to be in the 520-560 HP range.