We understand that Lat Long Alt can be derived from 3D Cartesian (X,Y,Z) but does a 5D Cartesian (X, Y, Z, Vx, Vy) does the extra mile to provide a more precise conversion to Lat Long Alt with the additional velocity data?
Welcome to PF.
Your question does not really make sense to me. The precision of the spherical coordinates of a point are determined by the precision of the corresponding Cartesian coordinates, speed does not enter the equation at all.
Perhaps you could explain the context of your problem and why you think the conversion is not precise enough for what you are trying to achieve. Sound a bit like there might be a moving object or vehicle involved?