There are a few reasons not to go E85...
The need for Jerrycans is one of the major ones since not a lot of regional centres have any E85 at all, so driving to Winton or DECA will use nearly a tank, then the track day, then the drive home...
I do 300+ peak hour km's each week in my car, I could easily switch to E85 (My pump can handle it, and my injectors are 550's... might need an upsize if I want to keep some decent overhead, I pass a few petrol stations with it each day), but its still the hassle of country trips which suck.
I'll do it in the future, but for now, I'm sticking to BP98