I always burn premium in everything. I've found that the difference MAY be negligible, but on extended review of mileage with each (premium 93 -vs- regular 87) I have noticed a mile or so per gallon improvement. (measured) This translates into LESS than the dollar COST of the premium, but when coupled with SLIGHT performance increase (I NOTICE a degradation with 87 octane... particularly in responsiveness and under HARD driving) it's worth the extra couple bucks a tank for the "good stuff".
On a side note, I've run a very HIGH GRADE racing octane boost formulation (NO lead, etc...) and found a MARKED improvement with the 'lara... (it's NECESSARY in the turbo Supra to prevent detonation at higher than pump gas boost levels, and rewards substantially under boost!) wherein when I went back to a tank WITHOUT the octane treatment, it even felt SLUGGISH! (I thought it was a problem, but realized I'd run a tank of gas through to empty and "purged" the mix... so added MORE boost and recovered from the sluggishness!)
I know most boost additives may be hype, but at about a liter to 10~15 gallons, this is a more serious formulation (for racing and such) and does seem to work... albeit meant for VERY high compression or BOOSTED cars...
NOTE: The additive I'm using is COSTLY and NOT a regular add in the Solara! Just an experiment, and I don't recommend it... but I DO use it regularly in the Supra when I want a couple extra PSI (and about 50 more HP!) so it's worth the $5~$10/tank to mix. (STILL cheaper than straight out RACE FUEL... although it is NOT as high an octane... only a couple points or so instead of a DOZEN octane.)
...anyway... been awhile since I posted much... and I always like to mix it up in the fuel grade controversy as I have some staunch beliefs after my well over a million miles of driving with a lot of experimenting along the way. At the end of the day, unless your car "NEEDS" the detonation preventing higher octane, it's a "preference" thing... but for those that recommend or REQUIRE it (i.e.: Supra...) it doesn't make too much sense to "skimp" and risk it.
G/L!
-crisp
