Which preposition to use with instructiveness

of Occurrences 2%

He was sought for the vigour and instructiveness of his conversation, and did use it largely as an instrument for the diffusion of his opinions.

to Occurrences 1%

[Footnote 8: See "Modern Currency Reforms" (1916), by E.W. Kemmerer, professor of Economics and Finance in Princeton University, for a detailed treatment of this remarkable series of monetary changes, probably unequaled in instructiveness to the student of monetary theory.

Which preposition to use with  instructiveness