The temperatures you mentioned are normal. You will find a lot of information on this in the archives.
Above 20mph, the cooing sytem does not need any additonal air flow from the fans.
Below 20mph is where the main and aux fans come into play.
It is possible that MB temperature gages are very sensitive and accurate while other automakers make the gages less sensitive to avoid unnecessary concumer concerns.
94 E320 58000 Miles