To be honest...
Since getting it remapped approx 2 weeks ago, I havent used normal 95 RON and have stuck with 97 Super unleaded. A mate of mine had a mk1 Focus RS and he used 99 RON a couple of times and said that it was like rocket fuel by comparison.. big difference but bigger price per tank too.
like I say, not tried the normal stuff yet but to be honest, just havent got round to it...but unless your using 99 I cant see that you would probably notice THAT much difference... Fuel consumption isnt a major consideration for me I have to say but I am not going to go out of my way to go get 97/99....... I may end up just alternating fuel I think where possible... you can read loads of stuff on forums about valves etc and problems in the long run with turbos etc not being run on anything other than Super, but I think I take that with a pnch of salt.
There was a recent write up in the motorcycle press regarding the new BMW S1000RR vs GSXR 1000 K9 and using different fuels... they tested a full tank of 95, 97 and 99 RON on the two bikes and only came out with like 0.5 BHP or something improvement over standard 95 RON... Of course I know that motorcycle engines are higher performance than a normal road car... but generally.... in day to day driving.... 95 would be fine.
Having said that.. for my own curiosit and from what I was advised when I got the car mapped: I WILL now subject the Coop to a tank of 95, 97 and 99 RON and let you know if I can notice any difference.
Give it a go yourself ??