The February edition of FII has a section on the use of MoGas in Aviation, and included in it is the availability of ethanol free Mogas. I can forward same to you if you wish.
On the issue of carrying some E5 and some nil, there has been alot of comment about this in the UK forums, and it would appear that most MoGas is sourced from singled blended sources, so they cannot state categorically that it is ethanol free.
Many microlights are cleared for E10 by the engine manufacturer, as Higgie states, technically there is no provision by IAA yet to clear use of E4, or above, although it is allowed in the UK for aircraft less than 450kg, if suitable approved by the engine manufacturer.
Strangely, a comment was made to me last week that AvGas is now known to contain ethanol! Anyone got further info on this?