Soldato
The performance between the two is very silimiar. Not many games support PhysX so no point really. For gaming CUDA won't be much of help.
I would stick with a 6870 as it leaves you with the option of crossfire. You can still use the bottom PCI slot if you add a second card, so maybe take out the soundcard and see how the onboard is for you first.
As for price drops, there is a possibilty that they'll drop when the 6900 series are released, but the chances of these happening are quite low, although the 470 is at a great price at the moment so it might pressure AMD.
I would stick with a 6870 as it leaves you with the option of crossfire. You can still use the bottom PCI slot if you add a second card, so maybe take out the soundcard and see how the onboard is for you first.
As for price drops, there is a possibilty that they'll drop when the 6900 series are released, but the chances of these happening are quite low, although the 470 is at a great price at the moment so it might pressure AMD.