5970=About the performance of a 7870.
So, literally yes. But You shouldn't do that. 1 6870 costs $170, the same as the lowest of 1GB 7850's prices and 2 6870 means $340. Which means $20 more than the 7950 itself. Plus, You also have hassles and issues with Crossfire. Like Micro-Stuttering, Games don't support crossfire, Driver Problems, Temperature Problems, High Power consumption, etc.
So, Only crossfire only when you have a 6870 with you and only got $170 to spend. Otherwise, no.