Around here no choice .
Some tuners carry a Ethanol test kit with them to see what percentage they are getting , it varies 6%-10% .
14.7 gas stoich , 14.12 is E10 stoich , E85 is like 9.7 stoich , E85 makes good power , high flash point (no knock) so you can run loads of timing and high compression , just have to dump a lot of fuel , oh and it is 105 octane .
O2 sensors switch back and forth to maintain Stoich or Lambda 1 , E10 will work with the O2 sensors range of switching . E10 sucks for carbed motors .
E85 flex fuel cars do more than just have larger injectors , the timing is altered as well as air/fuel along with 20 or so other tables .
Water is a major thing with E Fuels , they do attract water . Methanol will hurt rubber but not Ethanol , and the varnish thing is true , Ethanol does act as a solvent on it .
Most cars and trucks I have tuned were way rich in PE (power enrichment) mode (no power to rich not lean ) , 12.6 to 13.2 AFR makes good power in a NA (natural aspirated) motor .
E85 make for a good race fuel .

I wish we had more access to the ECU on our bikes , timing , air , we have fuel in a way that we can lean or rich the injectors (Power Commander) but still want more control over the ECU .
Just think Moonshiners knew of this years ago , think the Kennedy's .

My $0.02 on Ethanol .