I honestly seriously doubt that Killer is not able to pierce the RS, much less Zoro. It would be interesting to find out what would it happen with the former overall, anyway.
The suit is not nullifying damage, so that´s pretty obvious, but it´s baseless to assume until a certain level how high the AP needs to be so that it gets damaged by one attack.
King did not do it, and the attack was not harmless, something Oda expressed by Luffy getting worried and once again Sanji pointing out how sturdy it actually is.
We also do not know how it interacts with your natural durability, if it stacks up, or if it´s two distinct stats and so forth, though i would assume the former.
So any attempt to state an absolute statement at this point in regards to Sanji´s suit is only to comfort yourself really rather than be constructive.