Dual Video Card Question

[FrostyWalrus]

So I've got a Sapphire Radeon 6970 in my machine right now running solo. I'm considering buying a Sapphire Radeon 7870 to put in my machine as well.
I'm stuck on if I should buy the card and use it as a primary video card and make the 6970 a dedicated Physics card or if I should SLI them and
have them run together without the 6970 being Physics dedicated.

I know the basics of computer hardware, overclocking, etc, but I've never ran dual cards before. If the question doesn't seem to make sense, please advise me
on what I should do if I were to buy it. I can provide any technicalities if they are needed.

Thanks guys!

[K PhaNTOM]

Crossfire and SLI have to be the exact same GPU. You can't mix and match your cards. The whole idea of a dedicated PhysX card is not smart. Only a few games use PhysX and I'm willing to bet you don't play them. Buy the better card, replace the 6970 and sell it on ebay or to a friend.

[FrostyWalrus]

Fair enough. Thanks!