The complete stable phase diagram of the two-component system (heptyloxy)cyanobiphenyl (7OCB) + (octyloxy)cyanobiphenyl (8OCB) was determined by means of modulated differential scanning calorimetry (MDSC), optical microscopy, and X-ray diffraction measurements. It was experimentally established that the 7OCB + 8OCB two-component system exhibits a monotropic reentrant nematic behavior. A complete quantitative thermodynamic analysis, through Oonk's equal G analysis, was performed, including the calculation of the monotropic reentrant behavior and a discussion of the stable melting phase diagram. Moreover, the specific-heat critical exponents (alpha), through second-order SmA to N transition, was obtained. If these alpha-values, together with those corresponding to other systems sharing cyanobiphenyl (nCB and nOCB) compounds, are plotted against the normalized nematic ranges, a common and uniform crossover trend is found. This behavior allows one to predict, in a simple way, the order of the SmA to N transition.