You ask about E85. E85 is not the same as the typical gas (becoming more common all the time of gasoline with some alchol in it), it contains up to 85% of ethanol with as little as 15% gasoline.
Using E85 in the BD would require some major mods from fueling to possible fuel lines and other issues.
The Owners Manual indicates it is okay to run up to 10% ethanol mix in the fuel which would contain 90% gasoline, that exact opposite of E85. Two different animals. Though I have not see it, I would imagine that there may even be some gasoline mixes out there that contain up to 15% ethanol. If I was on the road and was in desperation mode of running out, and such with 15% was the only thing available, I would go with it but try to find the higher precentage of gasoline/ethanol mix as soon as possible-perferably gas with no ethanol. Unfortunately it is getting harder and harder to find.
Bottom line E85 is not good on a stock Big Dog, it is not a Flex Fuel vehicle.