The relative thermochemical properties of cluster ions (solvation enthalpies, entropies, and free energies) can be obtained from experimental techniques such as high pressure mass spectrometry and selected-ion flow tube mass spectrometry. Theory can play an important role in these studies by providing both accurate binding energies of the smaller members of the cluster families and insight into the structure and bonding in the cluster ions. This study assesses the performance of a variety of levels of ab initio and density functional theories for predicting the structures and energies of one family of cluster ions, the proton-bound dimers between HCN and HCN, NH3, H2O, and HF. The theoretical procedures were assessed based on their performance relative to high-level treatments such as QCISD(T) correlation, the 6-311 + G(2df,p) basis set, and G2 energy calculations. The results of the assessment indicate that MP2/6-31G(d) optimized geometries are sufficient for the calculation of binding energies and heats of formation with advanced methods such as G2. Further increases in basis set size and electron correlation improve the geometries of the dimers, but these geometric changes have little impact on the final high-level energy calculations. The heats of formation and binding energies of the clusters are best described by G2 theory, but modified versions of G2 such as G2(MP2) and G2(MP2, SVP) also provide reliable values. Calculated binding energies of these four proton- bound dimers are compared to available experimental values from the literature, and the effect of basis set superposition error is examined.