Notice how Shell dont actually claim an octane rating for Optimax on the pumps. I think I remember hearing that it was refined at 98.6 but they dont guarantee it on the pumps like super is listed at 97RON at other stations.
I avoid Optimax if I can help it. Car often feels sluggish on it and its more expensive, but Id rather use it than 95RON.
The Sainsburys near me has just refitted its petrol station, and as I was driving past yesterday I noticed that some pumps had 2 green nozzles........I was so intrigued (never seen a supermarket do SUL before) that I went back in and sure enough, they now do SUL in there too
. I think Ill stick with BP or Total if I can help it, but its handy in case Im in a rush. Im sure supermarket fuel comes from the same place as the rest - they probably just buy it from one of the big companies.