Our hemis aren't flex-fuel, and there's lots of variables involved, but for those that think they get better "performance" on pure gas, I wonder if it's real, or if it's because there's a little more pedal needed. Dyno tests I've seen (on FFVs) show no power loss with E85. As as said before, power actually goes UP, but by such a tiny amount that you wouldn't notice it. It'd be real interesting to see an actual dyno comparison on the hemi using pure gas vs. 10% ethanol.
I'm by no means an expert on fuels and ethanol....but I believe ethanol could be a decent fuel source however running it in an engine that is designed around gasoling does not justify it. I think ethanol has a very high octane rating (near 100 octane), so if you designed the engine with high compression and more timing advance, you could probably get more power out of it at the same cost for filling up the tank....I bet the dyno's you've seen that don't show power loss were tuned with more timing advance to take advantage of the ethanol's higher octane...
Ethanol free gas does get you much better mpg....my brother had a nissan sentra right before ethanol was introduced into fuels, and it was rated at like 40mpg hwy/30mpg city or around there...and it got it. The next model year ethanol was introduced and his 1 year old car was then suddenly getting 30-35 mpg hwy at best, and like 25-30mpg city. They have redone the ratings for mpg for vehicles due to this, and most have probably noticed that they have dropped...also my old s10 would get up to 30mpg on the hwy at slower speeds, after ethanol was introduced, 26mpg was the highest I ever saw after that, and that was on one trip, usually it was more like 22-24mpg.