  We consider proton decay in the testable flipped SU(5) X U(1)_X models with
TeV-scale vector-like particles which can be realized in free fermionic string
constructions and F-theory model building. We significantly improve upon the
determination of light threshold effects from prior studies, and perform a
fresh calculation of the second loop for the process p \to e^+ \pi^0 from the
heavy gauge boson exchange. The cumulative result is comparatively fast proton
decay, with a majority of the most plausible parameter space within reach of
the future Hyper-Kamiokande and DUSEL experiments. Because the TeV-scale
vector-like particles can be produced at the LHC, we predict a strong
correlation between the most exciting particle physics experiments of the
coming decade.
