The latest driver is a big improvement but neither AMD, nor Nvidia drivers have been able to make two cards look as smooth as a single card.
When I was running two 560's in SLI, the only time it felt as smooth as my single 780 feels, was when I was able to keep a game over the monitor refresh rate. (60fps in my case)
Once I dropped below that, it was not as smooth as my single 780.
I would go with a single 290x rather than crossfire.