Leaving aside the optimisations, I assume you are doing N^3 multiplication, whereas Strassen algorithm with complexity N^2.81 or even Coppersmith–Winograd algor

Leaving aside the optimisations, I assume you are doing N^3 multiplication, whereas Strassen algorithm with complexity N^2.81 or even Coppersmith–Winograd algorithm with complexity N^2.37 with larger constant is better with 5000x5000 square matrix.