Looking at the numbers, Forza is no wear near competing with GT in terms of sales, quality wise Forza is very good though. The prologue of GT5 sold 2 million so it all points to GT5 selling huge numbers. Say GT5 and Forza 3 were released the game month numbers should that Forza 3 would not stand a chance against Gran Turismo so it is once again the case where GT had no competition of substance. Forza is the main competition and at most it will take away 2 million sales at most from GT, cant see it doing anything else.