I have an '81 240D MT. I drive it to work every day. It shows 265K, but probably has over 300K. I have done a lot of work on it. Basically replacing ruber pieces, hoses, belts etc. Resealing or rebuilding or replacing water pump, vacuum pump, clutch cylinders etc. It replaced a '96 Ford Contour with a 4 cyl.
I am mainly on flat land. It is slightly slower than the Contour. There are a few places I need to watch traffic, when I pull out. Still, its not treably slow. I get 27-28 mpg on country roads. I think when the Contour was running good, I'd get 26 mpg. I think I got 28 mpg on the highway, while trying to keep up with traffic, 70-75 mph. When I slowed down to 60-65, I think I got 32 mpg.
Also, I almost hit some chickens this week. Not as bad as deer though. There were some on the side of the road. I went to the other lane or side. Another chicken darted out from that side. I locked the brakes. Both Chicken and 240D live to see another day.
Also, I wonder on the condition of these old cars and how that affect their speed. I did have trouble with the accelerator linkage, that limited my speed to 55 mph. It has been fixed, and I am happy with it for the type of driving I do.
Tom