We present new stellar velocity dispersion measurements for four luminous quasars with the Near-Infrared Integral Field Spectrometer instrument and the ALTAIR laser guide star adaptive optics system on the Gemini North 8 m telescope. Stellar velocity dispersion measurements and measurements of the supermassive black hole (BH) masses in luminous quasars are necessary to investigate the coevolution of BHs and galaxies, trace the details of accretion, and probe the nature of feedback. We find that higher-luminosity quasars with higher-mass BHs are not offset with respect to the M sub(BH)-sigmalow * relation exhibited by lower-luminosity active galactic nuclei (AGNs) with lower-mass BHs, nor do we see correlations with galaxy morphology. As part of this analysis, we have recalculated the virial products for the entire sample of reverberation-mapped AGNs and used these data to redetermine the mean virial factor left angle bracket functionof right angle bracket that places the reverberation data on the quiescent M sub(BH)-sigmalow * relation. With our updated measurements and new additions to the AGN sample, we obtain left angle bracket functionof right angle bracket = 4.31 + or - 1.05, which is slightly lower than, but consistent with, most previous determinations.