Any AFR based system will micro-stutter providing you hit a particular situation. That situation depends on the number of GPUs in the system along with the correlation between CPU and GPU render times. This is mathematically provable.
Maybe your tested scenarios did not meet these conditions, but that doesn’t mean micro-stutter isn’t inherent to AFR.
It’s kind of like saying 8xSSAA doesn’t have a performance hit because you run games at 320x240. Yes, in that situation it might be “free” but I don’t think anyone would agree that the “freeness” is inherent to SSAA.
I definitely wouldn’t bother with last generation multi-GPU though, not when we have next generation single card performance already available.
And there are a variety of settings one rarely considers when running SLI, and it's important to note individual game issues (and patches).
I've got SLI 560 Ti 2GB cards (OC, +50mV) with an i7 2600K @ 4.8GHz, 2x4GB DDR3, etc.
[3x1080p Asus IPS displays - 6060x1080 BC]
I had micro-stutter with BF3 at first, that seemed to be cured by turning off Hyper-threading (should have went with the i5 2500!), and then it seemed to creep back into existence, so I re-enabled it, and everything seems smooth now. It probably is still happening, in that there may be a few frames where there is a few extra #ms of delay, but it's not perceptible (even had a graph trying to see if it was happening, wasn't really noticing anything special in the graph). BF3 also had numerous patches, and there were driver patches (and numerous "issues" people had or didn't have with the 560 Ti cards in general).
In every game I've loaded up, once the graphical settings are configured to give me an acceptable framerate (based on game and need - I aim for 120fps in iRacing, 60fps in BF3 multiplayer, any intense single-player game as long as it's smooth and consistently over 30-40 I would be happy), I haven't noticed any further micro-stutter situations... I have noticed graphical stutters, but those are massive framerate drops in intense situations as opposed to "it says 60fps but feels like 15!"
I would argue it is likely a mathematical certainty in that it is always occurring, but how often (and with what games and/or system configurations/driver combinations) it actually occurs (constant vs a few moments) and whether it crosses the threshold of visual perception, is another argument entirely. That is truly a case of YMMV, because sometimes you get it and a few tweaks here and there will help correct it (can be hell finding out which tweaks are likely to help, as some, like disabling HT, most won't even think of unless someone suggests it/had positive experience with said tweak).
That said, with my setup, I have no choice. I decided to go triple-monitor when I built this system in October, and knew these possibilities going in. I am hoping to upgrade to better performance over the 560 Ti cards at some point, but definitely want at least 2GB of VRAM. Hopefully when the time comes, I can get decent cash for these cards.
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