  We fit a sample of 49 R=6000 NIR (0.9 - 2.5 micron) T dwarf spectra obtained
with Magellan's FIRE spectrograph with two different atmospheric model sets to
compare the derived physical parameters such as Teff, log g, cloud opacity, and
rotational velocity between the models, as well as their reliability. Many of
our T dwarfs have distance measurements, which allows us to calculate their
radii during the fitting, which can be compared to evolutionary models to
determine age, mass and potentially the presence of unseen companions. We
present our spectral sample and model fits, and comment on the measured
fundamental properties of these T dwarfs. Our analysis allows us to identify
global deviations between models and observed spectra, and hence provides
important feedback for the next generation of substellar atmospheric models.
