There have been several recent threads about ethanol. Here in eastern Iowa, 87 and 91 are ethanol free (<1%); and 89 is E10. There is one place in Davenport, 75 miles away, that has 93 ethanol free gas. Hard to find gas >91 around here, even with ethanol.
My Carrera seems to run fine on 91 (as does my BMW 530), but it would be nice to try a higher octane. The following web site says to avoid additives with alcohol or that are water absorbent. Lucas Octane Booster is the only one listed:
Is your gas additive safe with E10 fuel?