AMD fans, correct me if I'm wrong but from what I remember, a 5970 is not really two 5870 in crossfire. Actually, it's more like two 5830s in crossfire. Additionally, the AMD 5xxx series video cards did not scale that well compared to what's out now.
As for the OP...If the card didnt run OCed 24/7 untill this point then Id say its lifespan really depends on what you do with it now. But why not just get another 6950...when run in xfire they are more powerful than the 5970 anyway and your still going to have the same amount of Vram. Also cheaper and it will scale better if you decide to run eyefinity.
Edited by Racersnare21 - 10/22/11 at 5:27pm