High the RON the bigger the bang basically and it denonates at diff times.
i love a good bang 
And if "RON" was to receive one from you i guess it would be a "GANG BANG!"
oh and tesco is marginally cheaper down my way but i would have to drive an extra 20+ miles to get my fuel, sainsburys it is...
also on the point of RON i think its Research Octane Number - it relates to a the fuel being tested at a certain inlet air temp about 65 degrees and is different to a similar where as the inlet temp air is about 150 degrees and this is known as a Motor Octane (test) Number.
the diff btween the 2 numbers is know as the fuels sensitivity,its very important.cos todays engines differ so greatly its poss that a fuel manufacturer can come up with a fuel that has a high RON, but a lower than expected MON.
This mite explain why the numbers on the pump may b the same but cos different manufacturers hav diff blends one may perform worse than another. BUT the same company may make its fuel out of a different blend (different factory/different refinement end product/dilutants etc etc) to get the same RON but a different MON.
STILL WITH ME? im barely sticking with it...
but thats why in the US they have (wait for it) s third rating - the Pump Octane Number or PON rather than RON. which is something like the averag of RON n MON which givs a much better grade.
I think thats why its been reported that the Americans gas is sed to b not as good as ours - but its the same.
BUT even this system can n is abused with the addition of fuel octane boosters!
basically... sometimes the fuel from the same pump may be better than other times!
(a friend sent me an email a couple of years ago on this subject - exciting friend i kno... and this is just a summary...!)
also ive had a few beers and not re read what i typed so please feel free to correct me mistakes!
