Terminal outflow velocities as a function of star formation rate surface density for different choices of CR energy fractions, f_CR, and energy loading factors, η_e. The model predictions are compared with data from Heckman et al. (2015), which show measured outflow velocities for a sample of nearby starburst galaxies with stellar masses in the range log₁₀(M_*/M_⊙) ∈ [7.1 − 10.9]. Typical uncertainties are indicated in the top-left corner. The model with η_e ∼ 0.01 and f_CR ∼ 0.1 provides a good match with the observed data. Models with higher energy loading values (η_e) generally predict outflow velocities in excess of the observations. The transition from slow outflows in weak starbursts to fast outflows in strong starbursts is best captured by models with f_CR > 0.