Good news for anyone who's experienced the micro-stutter you can get from multi-GPU set-ups, AMD claim to have killed it completely in Crossfire scenarios with their latest Catalyst 13.8 beta drivers.
Micro-stuttering - if you've never encountered this foul effect - is frame rendering delay that occurs despite high average frame rates. Each frame in a sequence is rendered alternately by the connected GPUs and the juddering occurs because there can be variance between how long it takes for a given frame to be delivered. It occurs more frequently in CrossFire than SLI and, curiously, the effect is negated if you add a third GPU to the mix. Have the 13.9 drivers successfully banished micro-stuttering? If you're thinking "the answer had better involve some graphs" then prepare to not be disappointed.
The Catalyst 13.8 beta introduces CrossFire Frame Pacing - switched on by default - which ensure frames rendered across multiple graphics cards are displayed at a regular and even pace. It does this by ensuring there is a fixed delay on when a frame is delivered by a given GPU, which means that each frame in a sequence will be delivered with the same time constraints offering a far smoother experience.
There are some notable caveats though - EyeFinity users need not apply. CrossFire Frame Pacing is only available on single displays with resolutions up to 2560x1600, and won't work with any DirectX 9 games. So, Witcher 2 is right out. You can't see it, but my face is sad.
Anyone hoping to use multiple graphics cards to render high-resolution, multi-screen games (you mad, beautiful fools!) are still going to be stuck sucking up the dreaded micro-stutter. Well, unless they go for three graphics cards.