RE: Best oil content
I also blend my own fuel and note closely that the oil percentages recommended by the engine manufactures are MINIMUMS. In light of this, 20% oil content by volume is a decades long standing, proven oil percentage that will work well, and provide good protection in virtually all modern engines. Whomever stated that it was "false economy" to scrimp on oil (even a few percent) was absolutely correct.
Also agreed with is Downunder's comment on oil content not reducing power. Unless taken to ridiculous extremes...he is very correct, and I have proven this to myself. One might fine tune the oil percentage for a given engine based on it's application, but top end power tends to remain unchanged.
If you're using good oils....a 20% oil/vol mixture will keep you, and your engine happy for many, many seasons.
"BEST" oil content? Probably no definitive answer to that since it depends on a number of factors, but using the engine mfrs recommended MINIMUM oil content as a guideline....you should be able to arrive at a suitable amount to use on your own.