The present study compares the ability of two semi-predictive approaches, namely the Global Phase Diagram approach (GPDA) and predictive Soave-Redlich-Kwong (PSRK), to describe the experimental data in the binary homologous series of perfluoromethane-alkanes. Although this time PSRK is able to describe the patterns of phase behavior in the series under consideration, it fails to predict the data quantitatively. In particular, it underestimates the liquid-liquid equilibria (LLE) range for the light members of the homologous series and overestimates it for the heavy members. In very asymmetric systems, the predictions of PSRK are in total disagreement with the experimental data. In addition, because PSRK does not use the binary parameter l(12), it generates an incorrect slope of the LLE critical lines and isopleths in pressure-temperature (P-T) projection. In contrast, GPDA predicts robust results, even for very asymmetric systems, and yields precise description of the more-symmetric ones. These facts confirm a doubtless advantage of the approach that is based on consideration of the complete phase diagram and not only of its separate parts.