In SOCAL all you can find is 91 and lower...

 

I believe your dealer is either ignorant to octane ratings or trying to mislead you. European 2.7t owners may indeed be using fuel labeled as 94 octane, however that does not equate to 94 octane in the US. There are two methods of measuring the octane or knock resistance of a fuel, and they result in different numbers. One measurement is titled Research Octane and the other Motor Octane. Essentially the motor octane method places the fuel under higher stress (more heat and rpm) and results in a lower number (around 9 pts lower).

Fuel sold in Europe is classified by research octane only, whereas US fuel averages the results of both tests. Therefore, a 94 research octane fuel in Europe would be roughly equivalent 90 in the US. Next time you are at a pump look next the octane rating and you will see R+M/2 in small font, this designates Research+Motor/2.

In any event no production cars in the US are tuned to run on anything higher than 91 (because it is the highest pump octane available in many areas). Run 93 and you'll be more than fine.

 

In the US, in the summer, it is difficult to find any gas without ethanol. It is used to oxygenate the fuel and produces less smog when burned. Smog is a problem in the summer heat. The "problem" with ethanol is that is contains much less energy per gallon than gasoline, so a blend of 10% ethanol 90% gasoline will might produce a very small difference in fuel mileage for your car. It will be slight, in fact I doubt most people can detect it due to driving conditions change from tank to tank. Traffic, weather, driving conditions will overwhelm your best efforts to make a fair comparison. BTW, ethanol itself is an octane booster when blended with gas.

Octane boosters sold in parts stores do not contain lead. 93 Octane, highest available I think in the US is fine. I have noticed a very small performance difference between 93 and 87 in my 2003 A4 3.0L quattro, at least I think I have. But then again it could be in my head.

I think it is true that some fuels work better in different cars. find a fuel (Shell is OK) that works best in your car and stick with it if you can.

 

They have E85 at some stations, but it can't be used with out modifing a car. Since the ethanol is corrosive the gas tanks and fuel lines could fail. Some of the rubber hoses and parts are not compatable with E85. Also, E85 requires that the fuel injectors meter a greater amount of fuel than for gasoline with 10% ethanol.
So, while E85 could boost the octane, the car must be engineered for E85 and be a flex fuel vehicle.
If you really want high octane, liquified petroleum or compressed natural gas are other possiblities. However, there is the danger of having high pressure liquid or gas tanks. There are also very few service stations with these options, so the car would need to be able to still run on gasoline.

 

All octane does for your AUDI is prevent knocking and valve carbon buildup because it burns cleaner. The additives in Chevron/ Shell gas help further prevent any carbon buildup. If you add those cheesy octane boosters you are not adding liquid horsepower, you are not improving performance in any way other than maybe a few more MPG's on long road trips - and that is questionable. I have been putting Chevron and Shell gas in my Audi's for 10 years (92 Octane) and have never had carbon, knocking, or any performace issues. Stay away from the ARCO's, Texaco's and other small stations. 3/4's of the bottled crap you see in auto parts stores are just that - CRAP designed to take $$ out of your pocket. Put it this way, if you are relying on bottled additives to improve an issue or fix something, you have bigger problems. Now if your state only offers 91 or even 89 octane as its highest grade, it is due to altitude/elevation and should not be an issue for your car.