Bowie makes a lot of sense 😊
The hotter you run your engine the cooler the plug. So higher compression or higher boost then a cooler plug.
My experience is that if something is running rich or cool a hotter plug can clean it up. If things are getting too hot then too hot a plug can cause preignition, then a cooler plug can sort that out.
One thing I might add is that eBay is flooded with fake spark plugs, and some of them are pretty rubbish. There are even guides out there for how they subtly differ in appearance from the real ones - so my advice would be - be wary of the cheapest and look at the ones with reviews.
Ethanol burns cooler I’m told. Don’t know what difference it would make if you were to use it, either neat or mixed, Im afraid.