Pretty much everyone that has done the test has agreed to the fact that the ECU needs about 3 tanks. After that is the best time to drop back down to 87 in order to feel the performance loss.
A 22 cent difference is still less than $2.75 over the cost of refilling a completely bone-dry tank...less than $8.25 for three tanks (approx 1000 miles?) or less than $.00825 cost per-mile over regular...and that's assuming a 0% increase in mpg for the duration.
FocusFest 2013: Best of Show
Gateway FFW: Show Class Outstanding
September '13 ROTM