Driver Limitations And SLI-AA Mode
SLI, unfortunately, is not without its downsides.
If you're a fan of Dynamic Super Resolution (DSR) and Multi-Frame Anti-Aliasing (MFAA), two of Nvidia's new Maxwell-specific technologies, we have bad news for you: they are not supported in SLI under Windows 8.1. If you enable SLI, those options simply disappear from the Nvidia Control Panel. Users have reported that these do work under Windows 7, although we have not verified it ourselves. We asked Nvidia about driver support in SLI for both technologies and received the following answer:
"MFAA support for SLI configurations will be coming in a future driver release. DSR support for SLI is supported in some circumstances. More robust hardware configuration support will be coming in future driver releases."
What you do get is an SLI-exclusive anti-aliasing mode called SLI-AA that can be enabled through the Nvidia Control Panel. The company went back and forth on including this feature in its drivers. It was missing for a while and is back now. While you generally won't use it much, the option does allow you to essentially force MSAA on in DirectX 9 games that don't natively support it, and where you don't need the extra performance of SLI or where SLI AFR rendering is not supported at all. It won't work in DirectX 10 or 11 games, so the value of this feature in modern titles is negligible.
The above example illustrates the use of SLI-AA 16x compared to Blizzard's built-in FXAA support for Diablo III. You'll notice that SLI-AA produces a sharper image overall, but, like all MSAA-based techniques, does not remove aliasing from transparent textures (the banner, in this example). Click on the image to expand it for a better visual comparison.