The value of \( \displaystyle \lim_{n \to \infty} \sum_{k=1}^{n} \dfrac{n^3}{(n^2 + k^2)(n^2 + 3k^2)} \) is:
\( \dfrac{(2\sqrt{3} + 3)\pi}{24} \)
\( \dfrac{13(2\sqrt{3} - 3)\pi}{8} \)
\( \dfrac{\pi}{8(2\sqrt{3} + 3)} \)
\( \dfrac{13\pi}{8(4\sqrt{3} + 3)} \)