A systematic study of the pseudoternary system TbxNd y(FeCo)1-x-y is presented focusing on key parameters for magneto-optical storage applications. For compositions with perpendicular anisotropy at room temperature (x>0.08; 0.4>z+y>0.15) the Kerr rotation (λ=633 nm) increases with FeCo concentration for a given x/y ratio and increases also with the Nd concentration for a given FeCo concentration. The latter effect is more pronounced at λ=420 nm than at λ=800 nm. Room-temperature compensation is found at x=0.2 for all of these compounds indicating a Nd moment parallel and, in magnitude, similar to the FeCo moment. The high-temperature magneto-optical measurements revealed a significant lowering of the anisotropy constant at elevated temperatures with Nd concentration, which leads to a loss of square loops already 100 K below TC for certain compounds.