I've started using 90 octane in my 87 560 SEL and it runs fine. Mid-grade gas around here (Minneapolis, MN USA) is usually 89 or 90 at different gas stations--I just find one with 90, I mean, why get 89 when it's the same price. During the summer, I'll probably switch back to premium 92 octane (some have 93 octane) so it's running at it's best when the weather is good.
Are there any other ill effects to running lower then recommended octane other then pinging or power/milage loss? I just don't want to damage or pre-maturely wear the engine out or something like that.
2014 Tesla Model S (320 miles)
1999 S500 Grand Edition 164k
1992 300D 2.5 Turbo 287k
2005 E320 4MATIC wagon
1991 Alfa Romeo 164L 99k (sleeping for a while)
Then: 96 Lincoln TC, 93 Lincoln TC, 87 560 SEL, 87 300 SDL, 80 300D, 89 560 SEC