We've owned five 300Es over the years. We presently have a '90 and a '91, both with over 150,000 miles. We've owned the '90 for six years; the '91 for five. Both average about 22-23 MPG. The '91 gets a bit better mileage than the '90 for some reason. It'll do 26 on the highway.

We have never used anything but regular 87 in any of these cars.

No pinging. No damage.

IMHO, the compression ratio is not that high and then there's that resistor that retards the ignition 6 degrees (I took it out on one of the cars and still heard no pinging, but I was too chicken to leave it out)...