Will it surprise you that I you use about 100 gallons of the "old school" oil each year ?
Multi-grades were originally made in order to use up the light grade oils that were essentially waste products, thus reducing the price of lubricating oils.
Apart from reducing the load on the starter multi-grade oils offer noting, nada , nil , sweet f a , benefit over strait grades of oil.
So if you aren't trying to start in freezing conditions, there is little advantage.
In cars it is a bit different as to comply with EPA regulations engine must fire and start withing 2 complete revolutions so the thin oils allow easier starting.
The down side is the high temperature lubricating properties are totally dependent upon the integrity of the additive package and this is a difficult thing to qualify.
Synthetics are a bit different as their additive packages are a lot more stable than standard oils.
So basically you can run $ 20/ Qt synthetics without problems to replace the $ 4 /Qt standard grade oils .
But not the other way around.