When I test drove a 1988 300SEL a couple of years ago, I never got it on the freeway, but it does not seem like it was turning all that fast, but much faster than the 1995 GMC Suburban I had at the time.

My last Mercedes was a 190D and it revved pretty high over 55mpg (when compared to my Lexus of course). The Mercedes was a 4-cylinder of course.... I never had it over 60 mph, but it was right at 3000 rpms at 60 mph in 4th. If I recall, 2900 rpms to be exact at 60 mph.

3600 rpm at 65 mph seems quite high though, especially when compared to 3000 @ 60 mph on a 190D, which one would think would turn faster than a 300? I am/was considering a purchase of a 1988 300SEL, but if the engine is going to be going that fast on the expressway, I might have to reconsider.