Ok so I went and tested it.
With 347.88, I could not get SLI performance to work correctly no matter what.
Be it through standard settings, or Nividia inspector.

HOWEVER, 347.25 the first driver to support ffxiv dx11 actually works flawlessly so far for SLI and performance seems up a bit.
Might want to try that one out for people having issues still on 347.88