Just thought I'd share some info I recently discovered. From everything I can find out, it appears the fastest 300Es would be the 86-88 models. In 89, the gearing for 2nd gear was raised and 1st consequently lowered. Up until 90, all these cars (with exception of the wagon) used a 3.07 rear axle. In 90, the axle was switched to something around 2.89. 90 was the slowest year because it still had 2nd gear start. 91-92 got 1st gear start, making them a lot faster off the line than the 90, but the 86-88 could still smoke them pretty much. 93-95 got the M104 engines and a 2.64 (I think) axle in rear with 1st gear start. These were the fastest of anything.

In order of performance, I'd rank them like this (from fastest to slowest).

93-95 M104 3.2L - 300E 3.2 and E320
93 M104 2.8L - 300E 2.8 (and 94-95 E280 in Europe)
86-88 M103 3.0L - 300E
89 M103 3.0L - 300E
91-92 M103 3.0L - 300E
90 M103 3.0L - 300E

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1988 Mercedes-Benz 260E