The people that tell you that using higher octane fuel causes deposits in your exhaust, are the same people that will tell you to use the lwest possible octane rating, take the car out, floor it, and if you don't hear pinging/knocking your OK. The fact of the matter is that most newer vehicles, including Rodeos, have knock sensors, which sense when the engine is about to knock and retard the timing to prevent knocking. Thus many drivers of newer vehicles will never hear knocking. However, if the engine control system is retarding the timing, the vehicle performance (acceleration) may drop off a little. Switching to a higher octane fuel may improve vehicle performance slightly. Some vehicle owners manuals now state that the vehicle will operate on regular gasoline but may give better performance on a higher octane grade of gasoline. These engines are also eqiuipped with O2 sensors, which sense the air/fuel mixture of the exhaust just before, and sometimes after it reaches the catalytic convertors. If there is excess unburnt fuel in the exhaust, the computer leans the mixture being injected into the combustion chamber until the reading at the O2 sensor is within range.
Bottom line- If you can afford 93, don't think twice. If your strapped for cash, go ahead and get the 87, assuming that is the minumum required for your motor. Also have a look at your owners manual. Most of them will tell you to use higher octane for better performance right after they tell you 87 is the MINUMUM.
Brandon