Don't forget that the btu rating is per pound of fuel. Per pound of air you burn more e85. To compare the power output you need to correct for this, a stoiciometric mix of e85 and air is 9.765:1 (
http://ethanolpro.tripod.com/id213.html), petrol/ gasoline is 14.7:1 meaning you burn 14.7/9.765 times more e85 (1.5 times more). To compare the BTU rating you need to multiply the e85 btu value by this factor i.e.;
115,000 x 1.5 = 173,118
A decent increase, add to this that it cools the intake and hence you get a little more air and you get an increase in power! (That's assuming the engine is properly tuned for it.)
Edit: Fuel consumption will go up, economy on the other hand depends on the price of each fuel. Switching straight over with no change to the carbies it may be too lean to run properly if at all. Cold starting also worse, even with e10.