I recently did a highway drive to the Delaware shore from DC in my '01 E320 4-Matic wagon w/135k. Speeds ranged from 55 up to 77, AC off, averaged 45mph w/25.9mpg. No complaints from me.

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....just drive'em!
'89 300TE White w/Blue, 152K SOLD!
'93 300E Blue w/Tan, 154K SOLD!
'01 E-320 4-Matic wagon, 130K
'67 Vette Conv. White w/Blue, 217,421K