Looks like AMD has released their beta Catalyst 13.8 driver that includes frame pacing for better fluidity with Crossfire configs.
From the release notes:
Support for AMD CrossFire™ Frame Pacing
Frame Pacing ensures that frames rendered across multiple GPUs in a CrossFire configuration will be displayed at an even and regular pace.
Enabled through the AMD Catalyst Control Center; Globally or on a per application basis.
Frame Pacing is enabled by default.
Anyone with an HD 7XXX crossfire setup want to give this a spin and let us know how they work?