I have (2) 03 Tahoes that are vin z flex fuel. I rarely run E85 in them . Only to clean injectors. Octane rating has nothing to do with "power" in a standard low compression engine. You will not make more horsepower using 98 versus 95 octane. The octane rating is a calculated number used to represent resistance to detonation (Preignition/Spark knock). It sounds as E85 would be cheaper to run where you are. It just isnt mathematically here. Although you would have to go fill up more often using E85 because it takes more of it to go the same distance as it would with regular unleaded.
To give you an example. If you would use 20 gals of regular unleaded (liters where you are) a week to drive back and forth to work, you would use approximately 22-25 gals (Liters) running on E85 to drive the same distance.
Dont forget to convert yours to a vin z (flex fuel) you will have to change the PCM program (possibly the whole PCM), fuel injectors, rewiring of the harness going to the PCM and the fuel system mods like the fuel pump, fuel lines, most likely all seals too.
