maxalge :
Your mobo can only crossfire the second card at x4, on top of using an amd cpu with crossfire... Triple afflicted if you are not overclocking the cpu well.
I suggest you return the GPU, save some money and buy a single powerful card, preferably an nvidia card as they are less cpu dependant, then sell your original card.
I agree, a single GPU solution should have been what the OP pursued from the start given his motherboard, and AMD platform.
But that being said, the radeonPRO solution is a very powerful tool,
Tomshardware concluded in the article that "Aside from a few dropped frames and a handful of spikes when the test changes scenes, our dual-Tahiti card enjoys much smoother sailing.
In fact, the end result is often better than what you'd see from a single graphics card, with virtually no micro-stuttering left."
My point here is not that Crossfire is better than single GPU, because I still agree with you, but that he can minimize all his stuttering so that the two 6950s basically act properly like a single card.... but this requires properly setting up the RadeonPro stuff for every game
In theory none of those issues, (having an AMD CPU, 16x4x mobo) should cause stuttering, even though they will ofcourse lower his Avg. FPS. IMO The OP needs to find an optimal FPS point to set the dynamic V-sync at, something that is a little below the average and definitely below the monitor's refresh rate.