I think the torque depends on Mass, so the Big Fan would be the logical Contra candidate. But with OEI, the benefit would be a crapshoot.
Like the flying wing, Contra-Rotation of rotating mass(es) has been an obsession with engineers, and repeatedly fails to impress. It very nearly killed Howard Hughes, (Pratt), Steve Hinton (Rolls Royce), and with the wing, did kill Glenn Edwards.
Somewhere in a torque compensating system with contra rotation, relative velocities of rotating mass double. Heat, wear, inspection, complexity, etc. Worth it?
bear