  Aimed at identifying the role of microscopic Hamiltonian parameters on spin
wave excitations, orbital order, and magnetic moments in the $(\pi,0)$ SDW
state, two different three band models for iron pnictides are compared --- one
at two-third filling ($n=4$) and another at half filling $(n=3)$ --- both of
which yield qualitatively correct Fermi surface structure in the paramagnetic
state. Spin wave analysis of the model at $n=4$ shows instability of the SDW
state, which is attributed to weakly developed magnetic moments and weak
magnetic couplings due to overfilling, as inferred from the observed
stabilization of the SDW state and enhancement of magnetic excitation energies
upon hole doping. In contrast, the model at $n=3$ (half filling) yields a
gapped SDW state with well developed magnetic moments and the calculated spin
wave excitations are in excellent agreement with INS experiments. The sign of
the orbital order ($n_{xz} - n_{yz} \approx +0.2$) is also in agreement with
experiments. Both the zone boundary spin wave energies in the F and AF
directions as well as the orbital order are shown to peak near half filling,
highlighting the correlation between orbital order and SDW state stabilization.
