Hm, old thread.
I actually have tearfree disabled, but use kwin's "fullscreen repaint" vsync with opengl compositing with one laptop display and one DVI/HDMI display and I don't see any tearing with this setup at all.
But it's still not really stable, I have been getting random hangs for months.
But mostly it recovers fine after a few seconds. Only sometimes it's hanging the chromium gpu process and I have to restart chromium...
[drm] stuck on render ring
[drm] GPU HANG: ecode 0:0xf5f7fffe, in kwin , reason: Ring hung, action: reset
[drm] Enabling RC6 states: RC6 on, RC6p on, RC6pp off