Yep it varies depending on each car, my Stratus follows the energy curve almost perfect, the Impala does better with E85 than it should. Comes down to $/mile to me so E85 has to be 20% cheaper for the Impala or Suburban before it for me to use it or for me to play with blending again.
http://ecomodder.com/forum/showthrea...l-18896-3.html
Link to my limited testing