I would not poo-poo Honda branded oils. They are pretty serious engine builders. If they run it their race programs, it's likely to be very good oil ...
Another oil to look at is Mercury Quicksilver 25W-40. It's been a stable stout marine lube for a while and it holds up well in flat tappet boat engines.
Lastly, you can look at John Deere 50+ (not 50+ II) as it's 1200 PPM ZDDP and a very stout oil. See if your local Deere dealer has any old stock they will sell you

OBTW - 50+ was made by Chevron to JD's specs

Dunno who makes 50+ II ...