According to "mercedes500.de", the 560 does have a 2.65 shorter final drive gear than the 420.

Maximum velocity in the most powerful 560 was indeed 155 mph, or 250 km/h. High compression without the catalyst, of course.

Maximum velocity in a 420 was about 235 km/h.

After '87, the 560 could reach 240 km/h and the 420 reach 235 km/h. That's 149 and 146 mph, respectively.

So the 560 is faster by a few miles per hour. But it does have some serious weight to lug! 1830kg vs 1660kg for the 420. 3660 lbs for the 420, and 4034 lbs for the 560.

These cars are in Eural base format, I believe. So the 560 is loaded, and the 420 is not.

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1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)