Use what the manufacture says, dont cause problems (yes problems) and dont pay extra for higher octane.
In this case, use 87 octane unless the car starts pinging, then try to fix the problem causing the pinging.
If not working then go up one step to 89
Worse case try 93 and see if it ping goes away (some places sell premium grade as 91 or 92 or 93). Older hi mileage vehicles may get to this. Octane is you might say what is requied to eliminate knock or ping.
You would need to reprogam the computer to optimize the use of any higher octane than 87.
In isolated cases, your vehicle may run better with highter octane ratings, but that indicates there is a problem causing that to run better on that 89 octane.
When I had a 1984 Toy p/u 22R I used 88 or 89 due to mechanical issues causing the need for that.
I suspect the gas itself may have caused your difference (taking your word that there was a difference). Try 87 octane but with 3 brands of gasoline over a period of time, and simulate exact driving times, conditions and trips and see what yu get.
Check with Toyota master mechanics and their engineers for their opinions.
Read this article about a toyota 4WD:
http://experts.about.com/q/3147/4009318.htm
