Fully microscopic many-body models are used to determine important material characteristics of GaAsBi and InAsBi based devices. Calculations based on the band anti-crossing (BAC) model are compared to first principle density functional theory (DFT) results. Good agreement between BAC-based results and experimental data is found for properties that are dominated by states close to the bandgap, like absorption/gain and photo luminescence. Using the BAC model for properties that involve states in the energetic region of the BAC defect level, like Auger losses and free carrier absorption results in a sharp resonance in the dependence of these quantities for Bismuth concentrations for which the bandgap becomes resonant with the spin-orbit splitting or the BAC-splitting of the light and heavy hole bands. DFT calculations show that the BAC model strongly over-simplifies the influence of the bismuth atoms on the bandstructure. Taking into account the more realistic results of DFT calculations should lead to a reduction of the sharp resonance and lead to enhancements or suppressions for other Bismuth concentrations and spectral regions.