One thing to consider is that if you ride 2000 miles in a year...... running on premium will only cost $10 more than regular.......for the whole year.
In the US our available octanes are ...87...89... and 92. (racing
...105, 110, 120,and Avgas 100LL avail. also)
Twowheelers doesn't live in the US ( I think) and European octane measuring system is different from ours.... their 98 is like our 92 or 94 (or close).
Octane is a measurement of a gasolines ability to resist pre-ignition.
Pre-ignition is a gasoline 'lighting off' before the spark plug even fires because it is too volatile and will "explode" at a combination of heat and pressure alone (with no spark) like a diesel engine does (diesels have NO spark plugs or ignition systems)
Pre-ignition is also known as "knock", or "spark knock" and also "pinging".
An engine that is pinging will steadily (and quickly) get hotter and hotter till something melts (piston crown) or seizes.
So higher octane means you can run higher heat and compression without getting pre-ignition..... this is why high performance engines need higher octane and ping badly with low octane.... higher octane allows engines to be tuned for more HP without damaging themselves.
Which brings us to mopeds.... mopeds are low performance engines (in US) designed for simple cheap transportation.... they are not high performance and do not need high octane.... high octane will not hurt a ped engine (or any engine) there is just really no point.
One thing to remember is that mopeds are quite often ridden by kids... who might just put any gas in anything.... the engineers know this and make a moped so that it will not hurt itself with the lowest octane available.
But if you feel yours runs better with premium.... thats alright.. it'll only cost bout $10 more for a whole year of use.
I don't believe there is any more or less crud or dirt in any of them... they all get processed by the same equipment, trucks, and storage tanks..... a $2 inline plastic fuel filter is smart for any small engine.