The slope of \( 8x - 6y = 4 \) is \( \frac{2}{3} \) and the slope of \( 8x + 12y = -1 \) is \( -\frac{2}{3} \). The lines are neither parallel nor perpendicular.
Thus, the final answer is:
\[
\boxed{\text{The slope of } 8x - 6y = 4 \text{ is } \frac{2}{3} \text{ and the lines are neither parallel nor perpendicular.}}
\]