The takeaway from this analysis is that the accuracy obtained from these very large basis sets is comparable to what is possible using the somewhat more modest Karlsruhe basis sets. Unlike the case of SAPT0, once the slow convergence of the dispersion energy is taken out of the picture it is no longer the case that jun-cc-pVDZ affords the best results, and the accuracy is improved substantially in triple-ζ basis sets. The data provide no compelling reason to to push to quadruple-ζ basis sets, however. These "(3df,2dp)" basis sets were originally developed for MP2 calculations and provide relatively good performance for the hydrogen-bonded subset of S66, where large induction effects amplify the importance of polarization functions. For the other S66 dimers, however, the performance of these basis sets is nearly identical to that of several other Pople basis sets, notably 6-31+G(d). A set of diffuse functions is necessary even for the dispersion-bound complexes but otherwise the double-ζ basis sets perform just as well as the triple-ζ ones, for the dispersion-bound and mixed-influence dimers. Polarization functions matter little for dispersion-bound systems and affect the MAEs for that subset by 0.2 kcal/mol.