What's the life span on the 7800GT/X or 7900GT/X?

[Falcone]

I'm building a new computer and wanted to do SLi with either the 7800 or 7900 series. But upon hearing about the 8800 coming out in the next few weeks, I'm wondering if I should wait and just get 1 8800. Or go ahead the with 7 series in SLi. Anybody knows how long the 7 series will last? Any help is appreciated.

Thanks!

-Falcone