I have just been alerted to this newsletter (thanks cleverlever99), which
experimented with a 2003 Prius to see how it would run on E85 (85%
ethanol, 15% gasoline) as compared to using regular stock E10 fuel (10%
ethanol, 90% gasoline, the max amount of ethanol allowed according to the
owner's manual).

http://www.creedproject.org/stream_v7n2.pdf
Look on pages 1, 9-11

They did road tests (and dynometer testing), and calculated the fuel
economy and measured the output emissions. Emissions went down using E85,
but fuel economy was worse (lowered MPG). Emissions were worse during
cold starts. The E85 fuel caused the check engine light to go on (lean).
They did not study the long-term effects of the E85 fuel on the fuel
system (E85 can break down some components).