408 stroker fuel requirement?

At a freaking $1 PER GALLON difference between 87 and 93 these days it would kill me to have to be forced to run premium. WTF ever happened to 10¢ a gallon difference between grades of gas?
Then if I tune it for E85 type octane I'm also screwed as E85 is less efficient than plain pump gas ......
What's the most CR that could be reasonably expected to be happy with pump 87?