Honda Shadow probably ain't a modern engine at all, at least not covering the field all too well. A modern engine may check (some) viscosity and figure it in for actuators, pumps, I don't know what. Or just suffer one or another way without ever taking notice. Or be fine with it. Or see it as extra care under unusual circumstances. Or combine some of above within a road trip... Likewise not all points of lubrication within an engine are created equal anyway.
So revisit the chatter and follow into the examples and details, try to find out what you're actually interested in. A 5W-30 could be a common CK-4 most people would accept or could be FA-4 infernal stuff within the same grade. So just don't forget to take it far enough, once you awoke your first interest in viscosities. Otherwise most answers can't help.