You very likely will not tell any difference. Sometimes people find a blend of fuel that their car is more happy with and results in some better fuel economy, at least one active user on here who could comment about that and their car. A lot of times the additives are there to try and help with long term reliability issues more than anything else. Most of the big fuel companies are not going to comment fully on what their fuels should do because then opens up a can of worms about being liable for their claims.
I switched from "unbranded" fuel to Chevron years ago in my truck. Not because the truck ran any better/different but because I had spent quite some time with a Chevron testing engineer and discovered just how much dirtier the fuel I had been getting combusted at. But to see any negative effects from that more dirty fuel would take a LOT of usage, probably in the upwards of 150k or so miles. Since at the time I planned to keep my truck at least 300k miles it just made more sense to have the added piece of mind but that is all it is because I can't ever know for certain if the switch helps me any or if the "unbranded" stuff ever would have resulted in an issue for me.
Just be careful trying to run the car near dry on fuel. That can introduce air into the system and can cause more heartache than you'd want to experience. If you want to test out different fuels then I say get down to normal fillup levels and fill it up then try a few tanks of that fuel to see if any difference you notice and are happy with.
Last edited by Snipe656; 12-11-2012 at 11:43 AM.