Also - every shooter shoots with diff form and mechanics. I know guys that can shoot a 70# bow with 2117's and others that use 2018's or 2216's! Everyone is diff!
I used to subscribe to the theory that it's better to be overspined than under - so I'd shoot like 2117's or 2020's from my 50# recurve - and they were way over spined for ME. I can only shoot like 2016 or 2018's from my bow and have them fly right.
So everyone is just diff and if you read G. Fred Asbell's book 'Instinctive Shooting' he also notes the same issue as well....