Here is something to ponder
93 Vortec 4.3 Blazer
In town driving with 87 octane netted 14.7 MPG
Same driving only with 90 octane netted 17.0 MPG
Highway driving with 87 octane netted 15.8 MPG
Same driving with 90 octane netted 20.4 MPG
I didn't notice all that much difference in power and performance between the two grades, which sort of surprised me. However, the fuel economy stood out. With fuel prices constantly on the move, it is hard to put a cost analysis on it, but I'll try.
Around here, we have 87, 88, 89, 90, and 91 octane. Typically, there is .15 a gallon difference between 87 and 90 octane fuel.
Lets say my mileage remains true per octane used. At 15.8 MPG and fuel costing 2.15/gallon, driving 1 mile would cost me approx. .1361 cents using 87 octane. When using 90 octane and netting 20.4 MPG at a price of 2.30/gallon, driving 1 mile cost me .1127 cents. This is my highway fuel mileage expense.
In town driving yields the same results, showing 90 octane to actually cost me less per mile driven then 87 octane, but at a much narrower margin or .1353 cents per mile for 90 octane and .1463 cents per mile at 87 octane.
I bumped down to 89 octane last night and will run a tank full through, fill up again with 89 octane and see how the Blazer fairs with 89 octane fuel.