  We use the functional renormalization group method to analyze the phase
diagram of a 4-band model for the iron-pnictides subject to band interactions
with certain A_{1g} momentum dependence. We determine the parameter regimes
where an extended s-wave pairing instability with and without nodes emerges. On
the electron-doped side, the parameter regime in which a nodal gap appears is
found to be much narrower than recently predicted in arXiv:0903.5547. On the
hole-doped side, the extended s-wave pairing never becomes nodal: above a
critical strength of the intra-band repulsion, the system favors an exotic
extended d-wave instability on the enlarged hole pockets at much lower T_c. At
half filling, we find that a strong momentum dependence of inter-band pair
hopping yields an extended s-wave instability instead of spin-density wave
(SDW) ordering. These results demonstrate that an interaction anisotropy around
the Fermi surfaces generally leads to a pronounced sensitivity of the pairing
state on the system parameters.
