Perhaps to clarify;
225/60/16 is a great tire providing you have the correct offset rims to go with it.
I ran 225/60/16 up front and 235/60/16 in the rear on 16X8 ‘s.
It took me a long time, and lot of trial and error to get it right.
SEC can handle a much larger tire in the rear then the W126 sedan can, even though both cars appear to be identical for the most part, the Coupe crowd just seems to have a little bit more room under the wheel wells.
You also have to factor in, what condition your cars suspension is in, bushings springs and shocks.
The speedometer error was minor and live able in my car.
If you’re a purist, stick to the factory recommended tire size, you will not have any issues going that way.