Well, MS is the first logical explanation that comes to mind when someone uses AFR and complains about stuttering (I'm assuming here that his displayed fps are fine - maybe he could say something about that). I have a 580 SLI and I certainly know what I'm talking about. By your own admission, you never experienced/noticed MS, so - no offense - your opinion/experience on this is not really helpful. Forgive my lack of a better example, but it's kind of like a blind man saying "hey, that is not red, it's green".
I have seen MS in the past on older generation crossfire (5000 series) and uneven crossfire, and i'm pretty certain i've mentioned this in the past. I don't know where you pulled that from (by your own admission never noticed MS). I have seen it, but not on gpu's from recent years. 580 SLI, 680 sli, 7970CF, I haven't seen MS on any of those setups on single screen resolutions. I have never tried cayman in xfire, maybe it does have MS, that is entirely possible. In fact, it seems plausible because even techreport picked up some wildly varying frametimes on cayman cards, so I could be very wrong on this issue as to MS causing his problems. It doesn't exist on tahiti that i've seen, unless its specific to eyefinity or something.
I worded my earlier post rather poorly, apologies - Anyway, we can continue hypothesizing but i'm sure his issue isn't VRAM....I think we can probably agree on that and drop the issue. I didn't mean to create a tangent, my hypothesis is that his choppiness is resulting from the general weakness of cayman in DX11 titles and tessellation in particular. I could very well be wrong though, it could be MS. I'm not sure.