Most of us agree that it is wise to use an oil that is more robust than an automotive engine oil. One of the more robust oils will likely add many miles to the cam chain life, as well as other parts. Ordinary 10W-40 would be my last choice. Diesel engine oil is a good choice, and I prefer the synthetic for its resistance to oxidation, especially at the hottest points inside the engine.
Motorcycle specific oil is different than automotive engine oil, diesel engine oil, or racing oil. The question is where we really need that high priced stuff, and the answer seems to be that there are lower priced alternatives that give very good protection.
In very hot weather I prefer a 20W-50 or 15W-50 engine oil in our air cooled engines. The average sump temperature is one thing, but the engine needs protection at the hottest points.
Mobil 1 racing oil is specifically not for wet clutches due to some of the antiwear agents they use (probably certain types of moly). Chevron says not to use their Delo 400 due to the type of moly they're currently using. Other oils with other types of moly work very well. I use
Schaeffer oil with a big load of moly (and 0.15% zinc), as do the engineers at Schaeffer in their motorcycles, and we get excellent results. The Energy Conserving oils range from 0W-20 to 10W-30, so none will be in the 40wt range we need for these motorcycle engines.
Most full flow filters have filtration ratings in the 20 micron range, and that is usually good for long engine life. A bypass filter that filters down to the single digit micron range will give longer engine life, but the cost of the filtration system is hard to justify for most of us. (Despite their advertising, there are no sub-micron filters. If there were, they'd filter out the essential additives in the oil.) A supermagnet on the filter or drain plug is a very good idea. Industrial oil filters on parts with steel-to-steel contact, like gear boxes, often have magnets. Expect to see a black "mud" of iron particles too small to be filtered out. Hope you don't see anything big enough to be glittery.