We demonstrate highly efficient generation of coherent 420 nm light via up-conversion of near-infrared lasers in a hot rubidium vapor cell. By optimizing pump polarizations and frequencies we achieve a single-pass conversion efficiency of 260%/W, significantly higher than in previous experiments. A full 2D exploration of the coherent light generation and fluorescence as a function of the pump frequencies reveals that coherent blue light is generated at 85Rb two-photon resonances, as predicted by theory, but at high vapor pressure it is suppressed in spectral regions that don't support phase matching or exhibit single-photon Kerr refraction. Favorable scaling of our current 1 mW blue beam power with additional pump power is predicted. Infrared pump polarization could be used for future intensity switching experiments.