In the present work the analytical models are applied to calculate the system performance for different fibre polarisation mode dispersion (PMD) conditions and for varying system parameters and the results obtained with them are compared to those obtained using the discrete random waveplate numerical model (DRW) model, assumed as a faithful description of the real fiber with all order PMD effects. Through this comparative analysis, never done before in literature to the authors knowledge, the accuracy of the analytical models in the approximation of high-order PMD effects is studied, and, among them, a precise analytical tool for the system impairments evaluation is found.