For a long rod or cable,

longitudinal pressure waves propagate at the speed given by this formula:

Y is Young's modulus and ρ is the density of the material.

For a typical steel alloy, longitudinal waves propagate about 6 km/s.

Of course, this depends on the rod remaining in tension. If you push one end of the rod hard enough to reduce the tension to zero, the wave becomes transverse, rather than longitudinal, and the speed is far slower.