anything 30 weight and below in automobile oils have the friction modifiers that you want to avoid. 10w40, 15w40, 5w40, 20w50 will all work fine in wet clucth applications. And even then sometimes there is no issue. Most, but not all, people that have problems have problems with the clutch itself, not the oil making the clutch slip.
M1 does have a "reformulated" red cap 15w50 that I have not used so I can not say how good or bad it is. The older red cap 15w50 was a favorite among many motorcycle riders.
I have run golden spectro 10w40, mobil 1 mx4t (now called racing 4t) exxon superflo 20w50, shell rotella 15w40 and 5w40 in my zx9 with zero problems. I have noticed in MY bike and MY riding habits that the rotella line gives me better clutchless upshifts, better in my case meaning smoother, not as notchy as with the M1 4t. Rotella syn 5W40 is in there right now.
I have a case of Brad Penn 20w50 that I will be running this summer. But for all around best bang for the buck I believe (my opinion only) that the rotella 15w40 for the price and performance cant be beat. The price used to be $8.88 for the gallon jug (4 quarts) at walmart but has gone up to just over $9 now. I still believe it is an excellent oil that gives just as good a performance and wear results as the more expensive boutique oils.
Amsoil from all the rave reviews is an excellent oil to use. I do not use it as I change out my oil every 2000-2500 miles so it does not make sense for me to use it moneywise. Motul, fuchs silkolene, maxima are all good oils if you want to spend the money and are going to get your money's worth.
Mobil Delvac 1 is touted as a darn good syn oil if you can find it. The Mobil Delvac 1300 super 15w40 is a good one as well as Chevron Delo 400 15w40. I have a gallon of each to try out eventually. If you can find the Valvoline Synpower 20w50 on bogo I would not hesitate to use that either. I picked up 12 quarts last bogo.
Mobil 1 vtwin 20w50 from the specs shows it to be a stout oil with a darn good add pack. I would not hesitate to use it either, if I got it at a discount.
It is really up to you to decide. If you like to do the longer drain intervals then amsoil, M1, Motul etc... may be right for you. There are uoa's on here where some gold wing riders have gone as far as 8000 miles on rotella 15w40 with very good wear numbers and the report looked awesome.
If you want to run synthetics and change them out every 10K, 8K, 5K, 3K, or every 2K, it is up to you and your decision alone.