GWB characteristic strain comparison between default Croton16 and Bower06 models (η = 0.1 and f_edd = 0.01). Panel on the left shows models with time to coalescence up to 100 Myr, while on the right, the maximum time is 1 Gyr. The black line and blue diamond show the observationally constrained limit (PPTA; Shannon et al. 2015) and estimated SKA sensitivity (at the most most sensitive frequency), respectively.