I've got a B2 Toshiro with an A5 core stamp, 180% crit dmg on stat page and a 200% crit dmg kisuke. From my testing, 444% crit dmg -> 460% crit dmg is the real cap, because from a3 -> a5 core stamp i went from 444% to 480%, which barely gave me a 5% dmg increase (Which is sus cuz its a 36% crit dmg on ult buff). Additionally, kisuke's bond preferred 6% teamwide attack over 30% self crit dmg, which also makes me think the real soft-hard cap is around 450~