Been holding off finishing the game because how bad CFX scales for me. I heard SLI scales well in this game. I got Witcher 3 since launch and tested it with every driver since then. Up to a certain patch there was flickering but that was fixed. After game patch 1.07 CFX scaling was nonexistent. I could tolerate 45-55 fps @ 1440p but now that I moved to 4K it's really bad. GPU usage does not go over 55% for both cards and CPU is under 20%. What is odd is how the fps jumps. Never seen this behavior with other games. Just looking at something without moving I get 25 fps, 35 fps and 45 fps. Not sure if its a driver problem or game problem. The fact that SLI works lead me to bealive its a driver problem but then since game patch started this problem it could be the game. Either way this is my favorite game of all time and I think AMD should fix it before the next Expansion.
Edit: My friend over that Overclock.net explains the problem. It basically happened after patch 1.07 was released.