no lab evidence.

just the fact that I used to have to buy racing fuel in barrels in the US for my race engines which I can now comfortably run on 'pump' fuel here. I've also managed to advance the timing on most of my 'pump fuel' engines here and on my dyno they make more power.

I assume it's related to the average time fuel is stored in the US vs here. The octane rating falls considerably with a few months storage.

RON / RM/2 is just a different way to measure the same thing. 98 here is about 93 there. outside big cities in the US, its hard to get anything above 91 (~97RON) whereas in switzerland 98 is everywhere (and fresh because its actually used) and in most of europe 100 or more is also available at main outlets.

worth mentioning that I favour swiss 98 to italian 100. i've had some problems with italian 100. most likely due to it having sat for too long in the tanks.

A performance production car such as a 911 or M BMW will work safely 95 here but only because it has knock sensors that retard the timing. It will make more power on 98. Older engines that have been tuned require you to compromise on the timing (and hence power) if you want to run them on 95. If I ran 95 in some of my rally engines they would probably just blow a hole in the piston.

worth pointing out that there is more energy content in 95 than 98. unless the ignition timing is optimized for 98, you are wasting your time using it. I often see little old swiss ladies putting 98 in their aygos because they assume its 'better quality'.