The DSR+GSync+SLI limitation has become very frustrating and it is even worse now because at one point I was able to enable all 3 and as long as I was playing at the native resolution, Gsync would be enabled but if I wanted to downsample, I could change it to a DSR resolution and all it would do is disable Gsync. Now they've blocked DSR completely if you have Gsync and SLI enabled so I don't even have the chance to pick and choose what I want. This will be less of an issue when I replace my 1080p monitor with a 1440p monitor but for now, I'm playing Alien Isolation with a machine that is getting 250-450 fps when I completely uncap the framerate at 1080p. What a waste.
Have you tried GeDoSaTo?