  A $\chi^2$ analysis of several SUSY GUTs recently discussed in the literature
is presented. We obtain global fits to electroweak data, which include gauge
couplings, gauge boson masses, BR($b\to s\gamma$) and masses of fermions of all
three generations and their mixing angles. Thus we are able to test gauge
unification, radiative electroweak symmetry breaking, SUSY sector (- in the
context of supergravity induced SUSY breaking) and the Yukawa sector in each
particular model self-consistently. One of the models studied provides a very
good fit with $\chi^2 \sim 1$ for 3 degrees of freedom, in a large region of
the allowed SUSY parameter space. The Yukawa sector works so well in this case
that the analysis ends up testing the MSSM constrained by unification. Adopting
this point of view, in the second part of this talk we focus on the details of
the fit for BR($b\to s\gamma$) and discuss the correlations among $\delta
m_b^{SUSY}$, $\alpha_s(M_Z)$ and a GUT threshold to $\alpha_s(M_G)$. We
conclude that an attractive SO(10)-derived regime of the MSSM remains a viable
option.
