Preconditioned Total Field Inversion (TFI) allows QSM for the entire head and chest. The preconditioner determines the TFI convergence. Can we choose a preconditioner that maximizes QSM quality within limited computational time? To answer this question, we conducted two numerical simulations specific to these applications to search for an optimal preconditioner. We found that preconditioner too small or too big for a targeted susceptibility distribution would have less computational acceleration and consequently greater errors for a given computational time. Our results here suggest that the optimal preconditioner should be identified to match the image content.