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Using E85 in stock non-flex fuel engines with stock compression ratios results in lower mpgs, in my experience usually about 20%. Supposedly much if not all of that deficiency can be recovered by raising compression ratio high enough to be optimized for E85, which means that engine won't run well on regular anymore.
I live in corn country and E85 is almost always cheaper than the lowest grade of regular, sometimes by quite a lot. If E85 is more than 20% cheaper than regular I can run it straight and break even vs filling with regular or maybe even come out ahead. Now, knowing that running a 50/50 blend of E85/regular nets virtually the same mpg as straight regular (in my State that's E10) anytime E85 is less than regular I save money running that blend.
To directly answer your question, I don't have direct knowledge of whether a high compression engine burning E85 can equal the BSFC of a stock compression ratio engine running regular. Perhaps because ethanol is oxygenated a somewhat leaner mix can be tolerated.
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