We report initial results from a large Gemini program to observez>~5.7 quasars with GNIRS near-IR spectroscopy. Our sample includes50 quasars with simultaneous ~0.85-2.5 micron spectra covering therest-frame ultraviolet and major broad emission lines from Ly-alpha toMgII. We present spectral measurements for these quasars and compare totheir lower-redshift counterparts at z=1.5-2.3. We find that when quasarluminosity is matched, there are no significant differences between therest-UV spectra of z>~5.7 quasars and the low-z comparison sample.High-z quasars have similar continuum and emission line properties andoccupy the same region in the black hole mass and luminosity space asthe comparison sample, accreting at an average Eddington ratio of ~0.3.There is no evidence for super-Eddington accretion or hypermassive(>10^10 Msun) black holes within our sample. We find a mild excess ofquasars with weak CIV lines relative to the control sample. Our results,corroborating earlier studies but with better statistics, demonstratethat these high-z quasars are already mature systems of accretingsupermassive black holes operating with the same physical mechanisms asthose at lower redshifts.