SOURCE:
The Missile Defense Equation: Factors for Decision Making by Peter J. Mantle, Appendix C.

Mr. Mantle has come up with a set of "rules of thumb" equations that can be used for quickly coming up with order of magnitude figures for various classes of ballistic missiles lofted on minimum-energy/maximum-range trajectories.

While they may not be precisely accurate, they are mathematically and computationally "cheap" to run; and can get you into the ballpark with little information required.

In no particular order, they are:

Estimating the burnout velocities (V_BO) of Ballistic Missiles lofted on Minimum Energy/Maximum-Range Trajectories

Where:

V_BO: Burnout velocity of missile (km/sec)
R: Range of missile (kilometers)

Estimating the maximum time of flight (TOF) of Ballistic Missiles lofted on Minimum Energy/Maximum-Range Trajectories

Where:

TOF: Time of Flight of Missile (seconds)
R: Range of missile (kilometers)

Estimating the Apogee of Ballistic Missiles lofted on Minimum Energy/Maximum-Range Trajectories

Where:

Apogee: Apogee of missile (kilometers)
R: Range of missile (kilometers)