If you can get regular gas without ethanol, it will get better fuel economy, by approximately half the percentage of the ethanol that was in the blend you were using previously.
So, if you were using 15% ethanol, you can probably expect about 7-8mpg better, if you rejet to suit.
Ethanol has a stoichiometric ratio of about 9:1, and gasoline has about 14.5:1, so there's the difference. You use more ethanol to make power than you would use gasoline.
However, in racing situations where the compression is increased to take advantage of the anti-knock in pure ethanol or E85 ethanol/gasoline, and you use the rich mixture necessary, you can make more power with the alcohol than with gasoline. But, in street situations, using E10 or E15(the typical ethanol blends at the pump) will likely just cause you to get worse fuel economy.
The biggest problem for ethanol blends with the Iron Barrel is that rubber manifold hose that always disintegrates and rips from being eaten away by the the ethanol blend fuels. Using a section of heavy duty radiator hose helps to reduce the failure rate of that part.