105 is the minimum octane rating which the pumps are required to post for year-round. 85% ethanol blend is around 108-109 octane, the 70% which they should be blended at in winter gets down to 105 octane. The octane isn't that impressive compared to the MON value which is higher for ethanol than typical race fuel and the high MON value is typically where you see advantages in more timing and higher compression. There is a lot of unclear or wrong information out there so hopefully that helps clarify.