PRIMA is a cryogenically-cooled, far-infrared observatory for the community for the next decade. The PRIMA team is studying both a sensitive wideband spectrometer and a multi-band spectrophotometric imager / polarimeter. Key areas of study for the spectrometer include the trade between resolving power, wavelength coverage, and mapping speed for low-resolution spectroscopy (R~200), as well as the approach to medium-resolving-power spectroscopy (R~5000). For the imager, the number and wavelengths of the bands, the spectrophotometric channel width, and the approach to polarimetry are key trades under consideration. Performance estimates for the two PRIMA instruments are provided here and will be updated as the concept is further developed.