If you're encountering stuttering or hitching, try these settings. They work really well for me, but only for NVidia users unless AMD has equivalent settings.
1) In the Witcher 3 game profile, put max prerendered frames to 3, and power management to maximum performance.. Setting the max prerendered frames to 3 will increase input lag slightly, but it will make the game smoother as the CPU is now prerendering more frames ahead and keeping the GPU(s) busy..
2) In the graphics menu in the game, make sure the frame rate limiter is always set to unlimited. Using the frame rate lock increases the amount of frame latency from my experience.. One exception may be for those that wish to play at 30 FPS though.
3) If you have Vsync enabled like I do, use the in game version. It's better than the GPU control panel version in my experience in terms of keeping input lag to a minimum..
From my time with the game, it seems the stuttering is related to CPU usage more than anything. The game seems to have difficulty using the CPU for all the animations, physics and keeping the GPU(s) well fed.
A game like this should have much higher CPU utilization I believe, so it's something that CDPR will have to further optimize..