  We show that synthesis-induced Metal -Insulator transition (MIT) for
electronic transport along the orthorombic c axis of FeSb$_{2}$ single crystals
has greatly enhanced electrical conductivity while keeping the thermopower at a
relatively high level. By this means, the thermoelectric power factor is
enhanced to a new record high S$^{2}$$\sigma$ $\sim$ 8000
$\mu$WK$^{-2}$cm$^{-1}$ at 28 K. We find that the large thermopower in
FeSb$_{2}$ can be rationalized within the correlated electron model with two
bands having large quasiparaticle disparity, whereas MIT is induced by subtle
structural differences. The results in this work testify that correlated
electrons can produce extreme power factor values.
