I dont believe all the marketing bullshit. I put 95 RON in my zeds and the Gallardo and none of them have blown up.
Granted they may have been down a few bhp but I don't drive around the 'Ring everyday so would never, EVER, notice any difference.
This bullshit is the male version of what make up companies have been doing to women for decades;
"Ah, this super dooper face cream will transform you from the crack whore that you are, into Liz Hurley, all for £75 for a measely tub"
Any mpg gain is negated by the extra cost.