Adventurer rings were nerfed again.

Hey guys, I'm sorry if this has been posted up before but just to ask. I heard many people mentioning that the Critical Ring is better that Cruel Ring for attackers that already have Critical Shot / Throw. As both of the Rings seems to be similar to be, 1 with 1 WA higher, dealing 20% extra damage with 5% chance, while the other dealing only 10% extra damage but with twice the chance of 10%. May I just ask how is it that it is true for Critical Ring to be better? >< Like is there any calculation done to determine that?