Octane ratings around the globe are not the same. Some countries use RON ratings (Europe), some use MON ratings (US, partly or all states?) MON is typically 5 point lower than RON, so you should use at least 90MON octane leadfree gas.
Running too much octane rating does not harm an engine. That is why some modellers use AVgas, which I believe to be 95+ MON octane, a special brew for airplane combustion engines that have to perform at altitude..
Then there also is the gas mix. Depending on state, and state laws, some high octane numbers in leadfree gas are obtained by adding up to 15% ethanol. which may influence oil mix stability and Walbro membrane life.
If you can get 94 octane, by all means use it, as MVVS presribes a lower limit of 95RON octane, which equals 90mon octane. I use 98RON octane with good results.
Using a low 89rating is a risk for your engine, because detonation can set in long before you hear it. These detonation pressure peaks, also known as ping or knock, can seriously harm piston and conrod bearings.