Ta! Id left the search time at the default 1 month - duh!!
Read a load of posts and it looks like its subjective. I vaguely know someone who works at Shell so might ask for a definitive answer. On the station v supermarket petrol debate, she told me that filling station fuel IS superior to supermarket petrol. It seems there is less difference in price these days, so I tend to go to Shell or Jet.
Dare say Ill probably mix and match depending on convenience and price. At the mo, I have half standard and half bp ultimate. The guy at BP said that it shouldnt make much difference. If I had categoric evidence that using Optimax/Ultimate means more performance and mpg, then it might outweigh the (considerable) cost difference.
[Edited by Brooktop on 01 May 2005 at 11:22am]