I've had issues with a few titles whereby running on one 780Ti has been better than running on 2 in SLI when Gsync is turned on. Slight judder (not a total stuttering mess by any means) is the issue that's introduced, totally removing the whole point of gsync.
Quick summary of a few games with issues:
1. Dishonered. Unbelievably smooth with one card and Gsync. Using SLI very slight micro judder. Difference is night and day.
2. BF4. This is a weird one - Slight judder when running SLI when slow panning view around using xbox 360 controller. If using mouse the issue not really noticeable, and using one card only it's all fine.
3. Thief 4. Smoother with one card vs SLI with Gsync on
4. Bioshock infinite. Smoother with one card vs SLI with Gsync on
I did loads of testing and there's definitely an issue for some games, gsync and SLI. I should add that for most of my games there are no problems with SLI and gsync.
Also, what do you notice about most of those games I mention above with issues???????......
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UNREAL 3 engine in case you need a hint. I'm growing to hate this engine. It's getting old and it really needs to be dumped now by (lazy) developers. I bought the vanishing of Ethan Carter the other day, which is great by the way, but the entire experience is ruined by the loading stutter and judder that plagues you as you walk/ run around. This is not an SLI or gsync issue by the way, and I've tried every possible combo and fix out there, including running off an SSD, which never fixes these games with issues.
Texture loading judder is a well known fault of the Unreal 3 engine that seems present in every game using it on release until it's patched out. Deus EX HR had it until fixed by a patch, Bioshock Infinite had it really bad on release until fixed by a patch, Thief 4 had it until fixed by a patch to name a few (this is all regardless of gsync and SLI obvioulsy).
Some other findings of mine on SLI and gsync are in this thread somewhere a few pages+ back if anyone's interested
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