  We report measurements of Hc2(T) up to 85 Tesla on Ba1-xKxAs2Fe2 single
crystals and FeSe1-xTex films tuned by doping and strain. We observed an Hc2
enhancement by nearly 25 T at 30 K for the optimally-doped Ba1-xKxAs2Fe2 as
compared to the previous results and extraordinarily high slopes dHc2/dT =
250-500 T/K near Tc in FeSe1-xTex indicating an almost complete suppression of
the orbital pair-breaking. Theoretical analysis of Hc2(T) in FeSe1-xTex and the
optimally doped Ba1-xKxAs2Fe2 predicts an inhomogeneous
Fulde-Ferrel-Larkin-Ovchinnikov state for H//ab and T < 3-10 K, and shows that
Hc2 in multiband Fe based superconductor can be enhanced by doping and strain
much more effectively than by the conventional way of increasing disorder.
