Just in case anyone is travelling that way soon, BP has launched a 100 octane fuel in Greece called (imaginatively) "Ultimate". Should be just the thing to keep boost levels up in high ambient temperatures.
Optimax is similar but 98 RON as I understand it. Still a worthwhile difference especially cross country - Sainsbury's own version of it is just as good though and often cheaper (though not much). More for only a couple of quid extra per tank - well worth it IMHO.