Some of the voices, such as the professionally cloned voices with certain accents (Australian, for instance), sound best with the Turbo model. Additionally, the English V2 model offers more expressiveness, and I have an Irish voice for whom the accent only is able to come through with this model. I am probably not alone in this, and others will have voices that sound best with certain models. Also, Turbo specifically would offer lower latency so it would speak more promptly after the message was sent. Thank you for considering this feature.