To find the maximum and minimum values of \( f(x) \):
Take the derivative \( f'(x) \) and find the critical points.
Evaluate \( f(x) \) at critical points and endpoints \( x = -4, -3, -2, -1, 1, 2, 3, 4 \).
The maximum value \( M = 392 \) and the minimum value \( m = -216 \).
The value of \( M - m \) is:
\[ M - m = 392 - (-216) = 608. \]