In addition to performance bugs, there is also a new bug which breaks vsync as seen on vsynctester.com this makes all video including Netflix unwatchable due to stutter (60 hz instead of the correct 59.95 as before). Let me know if you experience stutter. Hardware is in signature and monitor is NEC PA241w.
In the nvidia control panel the refresh rate is correctly detected as 59.95 hz in 390 drivers, and chromium used to run at 59.95 with 387 drivers, but now it runs at 60 resulting in stutter.
System is Arch Linux with xorg 1.19.6, nvidia 390.25 and kernel 4.15.1