Hello,
GPU acceleration does not work in version 353. I do not know how is it possible. I get better performance with GPU acceleration turned off. In the previous version I had about 50fps(Good half window settings) when editing 4K video(mp4 AVC), in version 353 I have about 2fps with GPU acceleration.
I thought something went wrong in Windows, so I reinstalled the system. Still the same problem.
Windows 10, GTX1080