X-fire:
http://www.hardwareheaven.com/review...onclusion.html

Conclusion

The key aspect that we can take away from this 7970 CrossFire gaming evaluation is that AMD already have their new card on a solid footing. In all but one of the games tested we saw noticeable gains when adding a second 7970 and in every test we were able to play at 5760x1080 without any compromises in detail levels, most even with anti-aliasing.

It is also worth noting once again that the 7970 has advanced power technology which is able to power down our second card completely when not gaming. This offers considerable power savings over competing architectures where the second (or additional cards) draw power, even when in desktop mode.