RV630 can work in dual setups and we've seen GeCube dual card back at Computex. It turns out that some other companies from Taiwan that will get a green light to do that.
There is a design specification how to make this dual card and this will be the early preview of quad crossfire as you will be able to plug two of them and make them work as four cards. You will simply need a driver.
Samples should be ready late this month and some of these cards should be out in retail in early Q4, so sometimes by the end of October. This answers your question if dual RV670 card is possible.
Published in Graphics
Dual 2600XT comes this month
From several vendors