Saint-Venant's conjecture for pentagons

Let $\Omega$ range over planar pentagons with a fixed area, and let $T(\Omega)$ denote their Torsional rigidity. Saint-Venant's conjecture. Among all pentagons of given area, the regular pentagon achieves the maximal Torsional rigidity. This is presented as a famous conjecture about the shape optimizing torsional rigidity; the supplied text does not state whether it has been resolved.