Its not just the drivers, the game engine also needs to be optimized for SLI. At the moment with the latest drivers my cards will sit at about 75% usage rendering an average of 70fps. I have noticed however that under certain conditions my usage and fps drop (Heavy firefight and explosions). This could indicate an engine issue (IE needs optimizing). It could be due to the 4K resolution im running as there are render limits to a game engine. You can only assign so much memory and time to completing a set task before the GPU is required to render the frame. (Usually under 16ms).
So it might be a couple of patches down the road that they are able to squeeze some more performance out of the game engine.