Hi,
Refer to introduction to Crossfire/SLI thread, it looks like they can be crossfired.
The better card will be down clocked to match the 6570. Honestly not sure it's even worth it given not all games support crossfire.
If money wasn't an issue I'd tell you to go for it as it's probably a fun experiment
But really are certainly better off waiting however long it takes to save 30 more dollars, and see where that 60 dollars gets you by then, or maybe 90 dollars, a 660ti and even a 660 will dominate those cards