I have an 01 E320 and an 05 Crossfire Limited and they both run different with 89. I lose about 2-3mpg and noticeable power on the top end. My mothers CLK320 even triggers a CEL on 87 and it has happened more than once. 91 or better is they key with this motor and my MB tech tells this to everyone. I avg. about 2K miles a month and the MPG difference is enough reason to pay an extra 10 cents