Prius Gen 2 stumbling, cold start rattle, running lean? Blistered spark plugs, pinging when hot

I am struggling to understand exactly what you're trying to say here. Is E10 sold as 91 or 95?

Yes, adding ethanol has the same effect as adding octane, so the stated pump "octane" rating on ethanol blend fuel is not strictly stating the actual octane, but the equivalent as if only octane were used to lower the knock index.

In terms of only the Prius, I crunched the numbers, and for my situation, 95 costs less per km than 91. As I said, I get around 200 km more on 95. If you don't get 4.4 to 4.7 L/100km, then that will also make a difference.

Obviously, the cost calculation needs to be done to verify in different markets. Records of at least three tanks of each are needed, as relying on memory and feelings can trick the mind into believing anything.

 

We must drive differently, I've never achieved 4.7 L/100kms, except when running with the added range battery in place of the spare wheel and under tray storage .... then it dropped to 2.2 L/km and didn't drop any lower even when Jason (who owned the Prius before me) registered 2,200kms on 1/2 tank of fuel, our best was 1800kms on 40 ltrs, but a number of drives certainly required better than the 80km/h limit on pure EV mode, and longer than the 100km range the added battery delivered .....

T1 Terry

EDIT: Missed a bit, E10 is sold as just that, they don't advertise the octane rating but it is displayed at the pump in small writing ..... it would be a hard sell to justify the added cost per ltr between the lowest price fuel (2 c/ltr less than std unleaded .... sometime falsely advertised as 91 but actually says, in the same small writing, it is 89 octane) and the price they want for 95 or 98 ..... the E85 is outrageously expensive, but if you have a super car engine, you just have to pay the big $$
This might help explain the confusion Pump Gas vs Race Fuel vs E85: Which Fuel Is Right for Your Car? In Australia, E85 is exactly that, 85% ethanol ...... very expensive in comparison and te end of that video mentions how much of it is pumped into the intake on full loud pedal application ..... not quite as bad as nitro methane, but then that stuff was never intended for road use either .... but a nitro ethanol mix, pumped in at sufficient volume, really does make big power .....

T1 Terry

 

Neither does the other half. She struggles to get 5.0, and mostly the tank ends at 5.2 L/100km.

She does mash the go pedal more than I do, but other than that, I couldn't really say why we are different.