I highly doubt the post about 28 mpg in early 90's 300E's. Maybe at 60 mph. Now I grant that from '93 on there should be a couple of mpg improvement over the M103 engined cars.
My experience with over 200,000 miles on 2 different 124's, a '90 and a '92 is more like 22 to 24. Of course these miles were generally at 70 to 80 mph.

I would bet that newer C class would do better than 25 on the highway.

Steve