In the old '82 300SDT I can't remember worst mileage - it averaged mid-twenties always and I was relatively afraid of banging it against the limit for a long time (as it had 200k miles on it when dad finally passed it down).

On a California - Oregon trip recently I had my 190 2.6 well over 100mph for a full tank of premium and got only 210 miles out of it. Probably a good thing, as though I really enjoyed moving quickly (with my wife asleep at shotgun), the expense of keeping that pace forced me to keep it to a reasonable (read: ticket-avoidant) 80-90mph thereafter.