@Blue Albatross: Did you read the papers, which came with your certification?
I only know STC's with a big pile of paper, some filler cap sticker which answer the question already, and a paper to keep at the POH in the plane stating the same. On mine it says certified for Autofuel/UL91/100LL in any mixtures, both in the extended documentation and on the sticker. BTW - it also says Autofuel STC, not "Mogas" STC ...
Speaking of UL91, this is simply Avgas without the lead. This brew is much closer to the specs the old engine were built for, compared to 100LL - for which the old O-200/O-300 were never certified to run, though ;-).
"Mogas" usually is standard car gasoline with special overlooking to avoid ethanol in it. Even though some state the standard tap gasoline is not appropriate for aviation, I have my doubts that this is more protection of UL91 and Mogas business. Such as Total (selling Mogas) states there are additions for modern car engines in their premium plus gasoline, it may or may not have an effect on us. I was running an old O-300 on Aral Ultimate for a long time, which is ethanol free because they replaced it with ether and therefore covered by the autofuel STC, which was fine except for two thing: there is some yellow stuff not burning totally and spread over the place and the engine runs a bit hotter compared to Avgas, so you have to keep an eye on EGT/CHT.
One word to the ice on carb - yes, there is a physical evidence for something called Mpemba effect, which may cause Mogas run carb engines to encounter earlier ice pickup. The effect is more prominent at hot liquids, so this may also count for the temperature limits of using Mogas. Personally, I have run Autofuel (of various kind and sometimes dubious origin) in hot environments and never encountered that effect - though some bubbling trouble at hot&high.