I find I get better mpg on 99ron, it's Revo stage 1, with GP filter, PD160 intake and Miltek Cat back.
However I never really push it hard, there's no need 99% of the time, it just tears the tyres up!
And if I do want to prove a point.. few people seem to ever expect it to take off like it does
From all the research I have done, 99ron means the ignition timings can be slightly advanced meaning it will make a little more power, not that I have really noticed..I recently replaced the faulty N75 valve with a standard replacement, now that made a noticeable difference, no more wavy boost!
I think the main point about the 99ron is the fuel is better quality overall, some say the 97ron is just 95 with octane booster in it.(talking tesco's fuel).
The very best is Shell Optimax, but that is more money and not that much better than tesco 99 so tests have 'proven'.