RX's and Highlanders are mechanically the same and that goes for creaks and rattles that develop over time too. Only the cosemetics between the two vehicles are slightly different and everyone must make up their own mind whether the differences are worth the substantial price difference
Here in Minnesota, the State is presently testing and evaluating E85 conversion kits. I personally wouldn't risk using E85 until the conversion kits have been approved by a State or Federal agency or the automakers themselves.