We present results from constant-NPT molecular dynamics simulations of bi-disperse liquid crystal mixtures at a range of concentrations. These simulations are performed using the generalised Gay-Berne interaction potential. We observe that the transition temperature between ordered and disordered phases varies linearly with mole fraction. Also, the layer spacing in the smectic-B phase varies approximately linearly with mole fraction. We find that the region of nematic phase stability is very narrow in the NPT ensemble, but establish it for a single-component system. The difficulty in determining this region is related to the sensitivity of the nematic phase to density fluctuations.