I just finished a 734 mile trip with E85 in my FFV FEH.
I went east out of Colorado to Minnesota with 400 pounds of cargo.
Here are the stats:

Segment 1 (slightly downhill sections from 4700ft to 3000ft )
234.8 miles in 3.5 hours ~ 67 miles per hour ave. 60'F day
7.978 gallons = 29.431 MPG @ $1.999 per gallon

Segment 2 ( Nebraska, mostly flat, 3000ft to 2000ft )
180.8 miles in 2.6 hours ~ 70 miles per hour ave. 45'F mostly day
7.460 gallons = 24.236 MPG @ $2.389 per gallon

Segment 3 ( Nebraska to Minnesota, 2000ft to 1500 ft )
318.4 miles in 4.8 hours ~ 67 miles per hour ave. 30'F, headlamps on, heat on
13.700 gallons = 23.241 MPG @ $2.499 per gallon

Summary:

734.0 miles for $66.01 or 0.0899 per mile.
To beat that cost from pure gas, I would need to get 34.46 MPG.
Not likely @ 70 miles per hour in winter.

-John