If I were you I would look for a higher milleage one that has been well cared for. I own a 420SEL with 170,000 miles on it. I have owned it for two and a half years and have had to do very little in the way of repairs. I have all of the service records and from what I see most of the work was done between 100,000- and 150,000 miles. I think if you buy one around 75,000 you'll be buying it just as some major things start to wear out. For example, timing chains on W126 usually need to be replaced around 100,000 same with water pumps, etc. I can guarantee you that extra milleage on a well maintained SEL will not have any negative effects. My car runs like new. Its an 86, most people think its a 93-95 (They are obviously not familiar with Benz models, but then again most people aren't. If you can find one with a good service history you'll do well with a higher milleage car. The exhaust, brakes, cam shafts, timing chain, water pump were all replaced on my car in the two years previous to my buying it. I got a car with almost all new parts on it. If I had bought a lower milleage one, I may have had to replace all that stuff myself within one or two years.
Just my opinion..