I agree, it is a crucial point to get to know what we put in our tanks and "Mogas" requires quite some studies to do it right.
For example, I am running my O300 on a Petersen Autofuel STC - fuel allowed from gasoline taps for cars, with max. 1% Ethanol content and min ROZ 98 (EN228, ASTM D-439/D-4814, (ROZ+MOZ)/2 >87 octane). When I started to study the issue, I was amazed how few people knew ROZ/MOZ/Octane settings. In central Europe many times you can easily get "Super Plus/Premium" with ROZ 98, but you have to have a look at additives and ethanol (EN228 was changed and now has up to 5% ethanol, they tossed the E Zero signs ...).
At airfields, I am always a bit suspicious about the Mogas they give you - many times they do not follow the tap labelling requirements of car stations. I remember my last flight in Germany, where we found out by surprise, that they sold us ROZ 95 E5 as "Mogas", which is not what I would expect in a civilized country. Ok, may be disputable with civilization now there ... I did not really notice a difference in burning that in an old C172, except for some higher EGT.
I had a look at EGT/CHT and indeed, the O300 runs noticeably hotter on Mogas, with ROZ 102-98-85 in hotter running series. I hot summer I was running the engine very LOP, but this I can do with 100LL and 102, but with ROZ 98 I even get hot coloring in the painting of the back of the exhaust when going all the way LOP.