Interesting. It seems I've read that those tuned with an E50 blend are getting around 550hp, so if my thinking is correct, with increased RPMs, an E70 blend with stock turbos would likely surpass the 100 octane, but perhaps not significantly. Though with 100 octane at $9/gal the E70 would be much more economical in the long run, even considering the additional cost of the HPFP and injectors, and likely produce more power. Higher flowing turbos would, of course, also help.
Please feel free to correct me if my thinking/theorizing is incorrect.