Effects Of Using High Octane Gas In 1.6 L Motor (2011 Base Model Soul)

   we have been using 93 octane gas in our 2011 kia soul 1.6 l motor, 5 spd. ( currently at 31K mi.)  we have noticed more power especially when starting out from a dead stop---more torque.  our gas milage has also gone up about 1-1.5 mpg.  we do NOT use no name gas, but stick with major companies: sunoco, shell mostly.  -->when talking to some of the technicians at the dealer, they advised against using higher octane fuel than the lowest fuel the car is designed to handle---something about "confusing the computer", resulting in resulting in possible carbon buildup due to the computer trying to compensate, and predetonation, loss of power, lower fuel economy, etc, etc.     my understanding of octane is that it is a measure of antiknock property---how smooth the flame front spreads during combustion.  the higher the octane, the smoother the push, the more useable the power imparted to the piston, hence more torque, better fuel economy.     my understandind is that the highest octane fuels--(from the major refineries) have the best/most additives--(detergents, etc).  i talked to a tank truck driver who was delivering at a shell station.  he told me that at the refineries there are 2 tanks one can load from, the cheap tank and the premium tank.  there are 2 tanks at each station also.  when a customer buys anything BUT premium fuel, the gas from both tanks is being blended at the pump.    what is the REAL story here? i understand how using to low and octane gas can hurt an engine not designed for it.  how could is be possible for the reverse to be true? --or could it even be so? THANKS!  dave