I have used Amsoil Metric 10W30 motorcycle oil, (not their 10W40), in a 21 HP, Kawasaki engined, air cooled, Cub Cadet for two summers. I used it 1) because I had it on hand and 2) "Just because" I believe overkill is a good thing. I found it to be outstanding and a better product than Mobil 1 Racing 0W30 that I used the previous year (for the same reasons). Of course I have no UOA's or specifications to compare the two products, just how it ran, and how it looked at the end of the year, when I drained it. It also performed well in my Honda EU6500is generator.
The only other Amsoil products that MAY be better, are their small engine 10W30 & 10W40 oils, but I doubt it.
Life is too short, so go for it and use it!