There is no benefit to running more than e25 as that allows the car to pretty much hit the timing. When it is really hot out the IAT gets too hot and the car will not be able to hit its max timing even with unlimited octane as high IAT switches maps to lower targets. So 3 gallons mixed is pretty perfect.
I wouldn't do it with a supercharger as the fuel pump would really stress.
I really would like to see ESS or someone to a e30-e35 tune which our pump easily could handle and than take advantage and hit a few more degrees timing. Although 34 degrees with a tune now may give the maximum power per cycle anyway. Increasing timing does not always lead to more power. The cooling effect could continue to be realized with more e85 I guess.
I think the car is perfect with a tune (like ESS) and running e25. You get a car pulling hard like it should hot or cold. The car would bog so much in heat before this was not enjoyable driving it.