It only uses 10-15% more at cruise. (Some tuners tune it even less) It is a good idea to upgrade your fuel system to more capacity for WOT. 40% is just a reference as far as a fuel system upgrade.So if it requires 40% more fuel, doesnt that offset the cost?
And yes, even running a little more fuel is much better than running race Gas @ $11-$16 per gallon. It even outperforms race gas in most cases and you can get it at the pump without worrying about storage or the lead ruining your O2 sensors.
There are many, many advantages to running E85.