I would not run any other gas but premium in any MB. For one the engine is built and designed for it, and two the owners manuel will tell you running cheap fuel (refinement wise) will cause problems.
Living among refinerys and working in the petro-chemical industry its a known fact that the premium fuel is refinned or pureified for a better word to a higher level. And as you pointed out more of the additives content.
It would be like having some polluted water, that you ran through a filter (good one) and then said here to drink. The next one ran through that filter as above an then another and still one more filter after that. Which water do you want to drink? The first or the last one. I know this is not the best analogy, but you get the picture.
1989 420SEL 105575 miles
1990 Chevrolet E-Cab C-1500
1989 Olds Toranado Trofeo'