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Full Idea
To the extent that there is any conventional wisdom about the question, it is that S5 is correct for alethic logical modality, and S4 correct for apodictic logical modality.
Clarification
'Alethic' concerns truth; 'apodictic' concerns proof
Gist of Idea
General consensus is S5 for logical modality of validity, and S4 for proof
Source
John P. Burgess (Philosophical Logic [2009], 3.8)
Book Ref
Burgess,John P.: 'Philosophical Logic' [Princeton 2009], p.65
A Reaction
In classical logic these coincide, so presumably one should use the minimum system to do the job, which is S4 (?).
Related Idea
Idea 15417 Logical necessity has two sides - validity and demonstrability - which coincide in classical logic [Burgess]