API 6A has recommendation in regard with production specific level PSL.
NACE MR 0175 has specs for sour service and other materials used in corrosive environments. Based on calculated partial pressure some companies might have other (usually more stringent)requirements on material used.
Provincial and government regulations have to be taken in account as well. In AB, a critical sour well has to have a PSL3 WH, even-though API 6A recommends a PSL2 WH.
If you speak with WH manufacturer they will know this stuff and head you in the right direction.