RE: Best oil content
My personal preference is 20% oil for the majority of engines. For a bushed crankshaft I'd go up a bit more to 22%. If you want to experiment on using less oil then I'd suggest getting a thermocouple and checking the head temps. If it suddenly rises then you haven't got enough oil. But really I think it's false economy to go away from what's known to be a safe amount of oil because the cost of the small additional oil to go from 15% to 20% compared to the risk of quickly wearing out an expensive engine doesn't make it worthwhile.
You don't gain any power by reducing the oil content because the needle valve only tunes for whatever amount of methanol the engine needs. In other words, if you add oil then you open the needle slightly to account for it and let the same flow of methanol go through.