Yes, PhysX can make a dramatic difference if you play those games that feature it. The big difference between the two cards is that the 6870's are all reference models. For the GTX470, there is a lot of variety with different designs and custom heatsinks. If it were me, I would go for the Gigabyte GTX470 Superoverclock with the custom Wind Force III cooler. It will run faster and quieter than any 6870. The MSI GTX470 Twin Frozr II is another option. Both will give you PhysX to play Mafia 2, Metro 2033, Unreal Tournament III, Batman: Arkham Asylum, and a few others.