Personal attacks are such a kind response to those seeking helpful information. Some of us use fuels other than premium because it gives better performance, some because they can't get their preferred fuel.
Octane is all about compression, higher octane allows the fuel to be compressed more before it explodes. It is by no means settled that all Mercedes require the use of only premium fuel. The 12 cylinder V12 has a surprisingly low compression ratio of 9.0:1, lower than a 2006 Chevy Malibu which comes in at 10.4:1 with a recommendation to use regular. My 1991 300E has a compression ratio of 9.2:1 and runs better, in all regards, on mid-grade rather than premium.
One of the posters to this thread often recycles many popular myths about octane and the supposed ill-effects of running less than premium in a MB that routinely resurface on this board--killing catalytic converters, fouling injectors, destroying pistons, poor mileage and performance. Not happening. People are mostly repeating hearsay. Knowledgeable experts agree that lower octane will not damage a vehicle and that it is likely to have little impact on performance.
The biggest determinant of a fuel's impact on a vehicle is quality, and it should be noted that the detergent quality of a particular brand of fuels is likely to be identical across their product line. Bad tanks and low quality suppliers can, and have, made a big difference.
Most all of the user comments on octane I have seen on this forum have been opinions based on personal experience, usually second-hand and anecdotal. Few users are citing data and fewer still are acknowledged experts. As one poster to this thread says in his signature: "One anecdotal story does not constitute a statistic."
One of my previous postings on this topic, found here
, cites experts ranging from a well-regarded participant on this board to senior people at Mercedes, Porsche and the Society of Automotive Engineers. I believe it's worth reading.