There is no difference in performance. The higher the octane rating, the more resistant it is to detonation. unless your car is tuned to run premium, stick with regular.
If you run 93 octane in a car designed for regular, not all that fuel is going to be burned in the combustion process. Yes, your car will idle a little smoother, but a lot of that fuel is just gonna burn in your cat or go out the tailpipe. not very smart, especially with gas being so expensive these days.
If the engine has high compression, or the timing is advanced, you may want to raise the octane a bit. if you reprogram your ECU, run a stand-alone or get a chip (a real chip, the kind that actually has a new program rom) then you want to run a higher octane. Otherwise, stick to regular for sure, or it's just money down the drain.
GTS owners are advised to run 91 octane or higher, Best results seem to come from 93 octane, but in the GTS, the manual suggests 91 or higher (meaning, you can go as high as 100 octane, since anything more will be leaded fuel)
Hell, I remember when people were flipping out in the 70's over the gas crisis. Fuel prices got as high as $1.65 a gallon.
These days, fuel costs are even higher, yet people don't seem to care one bit this time around. They buy SUVs and don't seem to have a care in the world...
Just wait until you start seeing gas station lines that reach around the block, and they start rationing fuel; it'll be the 70's all over again, but people are still oblivious.
Honestly, if your car can run regular, run regular in your car. Only put something higher in if they are out of regular at the station. anything more is just wasteful, and believe me, nobody misses it until it's gone.