AMD has stuttering issues with crossfire, and I have zero ideas why they can't improve it. When I (and many others) can vastly improve the experience by just using a framerate limiter, why the heck can't AMD figure out what the problem is and fix it? Makes no sense to me at all...
If it's so easy to fix, why don't you do it? It's not as easy of a problem to solve as one might think it to be. nVidia has the same problems in multi-gpu setups as well and all it has to do is how long it takes for the the second card to render and sends its frame buffer to the other card. The problem is one card always has a leg up when one is master and drives the display because it takes time to send that data from one GPU to another. Now this goes very quickly, Less than a millisecond, we're talking maybe a couple hundred nano seconds, but that's added time that gets put on top of the rendering load that slows down that second frame. So what you have is it alternating between one frame rendered a little faster and the next rendered a little slower, and this difference between each frame is the stuttering you're seeing.
There was a review on another site the showed jitter and that running 3 cards in crossfire had less jitter than 2 and I would hypothesize that it happens because two of the three cards has the latency introduced because of the crossfire bridge and one gpu being master. So what happens is two out of 3 frames render in about the same amount of time with 1 frame getting rendered slightly faster. So the frame rate jitters less often than with two cards.
So since you have a frame rendering where you do not know how long it will take to render, then the next frame that might render more quickly or slowly than the last frame depending on what has changed on top of the added latency of the crossfire link and the master handling the frame buffer. So you tell me, how do you make that jitter less? I suspect both AMD and nVidia have programmers and engineers thinking about it but it's a tough problem, so don't go blaming either company for their multi-gpu short-comings because it's not an easy problem to solve at all.