Large supramolecular complexes examined in this work are presented in Fig. . We use standard data sets including S66 (not shown in Fig. ), S12L, and L7, and we augment the latter with a "buckyballin-a-ring" (bbr) complex, C 60 @[6]-cycloparaphenyleneacetylene). Several of these large complexes exhibit differences exceeding 1 kcal/mol between diffusion Monte Carlo and CCSD(T)/CBS benchmarks, even after accounting for the uncertainties in either benchmark.