Metastability exchange optical pumping (MEOP) is experimentally investigated in ³He at 4.7 T, at room temperature and for gas pressures ranging from 1 to 267 mbar. The 2³S - 2³P transition at 1083 nm is used for optical pumping and for detection of the laser-induced orientation of ³He atoms in the rf discharge plasmas. The collisional broadening rate is measured (12.0 ± 0.4 MHz.mbar^-1 FHWM) and taken into account for accurate absorption-based measurements of both nuclear polarization in the ground state and atom number density in the metastable state. The results lay the ground for a comprehensive assessment of the efficiency of this method, by comparison with achievements at lower magnetic field strengths (1 mT - 2 T) over an extended range of operating conditions. Stronger hyperfine decoupling in the optically pumped metastable state is observed to systematically lead to slower build-up of nuclear orientation in the ground state, as expected. The nuclear polarizations obtained at 4.7 T still decrease at high gas pressures but in a less dramatic way than observed at 2 T in the same sealed glass cells. To date, thanks to the linear increase in gas densities, they correspond to the highest nuclear magnetizations achieved by MEOP in pure ³He gas. The improved efficiency puts less demanding requirements for compression stages in polarized gas production systems and makes high-field operation particularly attractive for magnetic resonance imaging of the lungs, for instance.