The optical properties, of selectively aggregated, nearly single chirality single-wall carbon nanotubes were investigated by both continuous-wave and time spectroscopies. With reduced sample heterogeneities; we have resolved;aggregation-dependent reductions of the excitation energy of the Si exciton and enhanced electron-hole pair absorption. Photoluminescence, spectra revealed a spectral splitting of S(1) and simultaneous reductions of the emission efficiencies and nonradiative decay rates. The observed strong deviations from isolated tube behavior are accounted for by enhanced screening of the intratube Coulomb interactions, intertube exciton tunneling, and diffusion-driven exciton quenching. We also provide evidence that density gradient ultracentrifugation can be used to structurally sort single-wall carbon nanotubes by aggregate size as evident by a monotonic dependence of the aforementioned optical properties on buoyant density.