I've been a strong advocate of 20:1 fuel/oil ratio, but others have spoken glowing praise of 50:1 or even 100:1.
Even at 50:1, a percentage of cooling is lost as there is far less oil to absorb heat, a particularly important aspect when travelling at 5 miles an hour on a 100 degree (40 degrees celcius) day with the engine struggling it's guts out on a steep hill and virtually no forward air flow - it's cooking away and the oil is playing an important part in removing heat.
I'm not sure how the engine would cope with that scenario at 100:1
I've never had plug fouling issues with 20:1 and that's using an NGK BP8HS
The only time i've noticed the BP8HS struggle to stay at operating temperature is when idling for a long time whilst cleaning and lubricating the chain.
Oil naturally falls out of suspension and settles in the crankcase and when the throttle is opened the plug gets a good oil wash and struggles to clear it's throat blowing it out the system- that's the worst it gets.
Fabian