I've yet to see a non BS screenshot of Forza 3 showing better car models than GT5P. I agree that the environments are better detailed in Forza 3 though...although I'm comparing GT5P with Forza 3.
Prediction (June 12th 2017)
Permanent pricedrop for both PS4 Slim and PS4 Pro in October.
PS4 Slim $249 (October 2017)
PS4 Pro $349 (October 2017)