To really see a difference in the fuel economy you will need to run it for ~1000 miles or so to allow the ecu to recalibrate to it a bit, you will notice more responsiveness right away though. I went from 87 to 91 and wont go back. It seems to be a little more responsive, I dont hear the rasp as much on the exhaust, and it will help with less knock. I have also seen a 2 mpg jump in economy even when driving it harder, Ive been running it for a little while now. My only concern though is that I seem to be running a bit rich and burning off some extra fuel. I wish GM would offer a new tune for the v6s that want to run premium because tuning it to the higher grade fuel would help quite a bit, but doing it on our own voids warranty
Btw I prefer to run no ethanol, give this site a look, I have two gas stations in my area that run no ethanol...I dont always do it, but I prefer to when I can
http://pure-gas.org