Comment 92 for bug 114520

So at the time you did the sysrq-trigger command over ssh, Xorg was running with high CPU usage? Strangely enough it doesn't appear in the the trace output, which otherwise seems to be complete this time.

For returning to the old versions, I described it on the wiki page.

There is one upstream bug on 9200/9250 PCI cards, https://bugs.freedesktop.org/show_bug.cgi?id=10874, but there it crashes only after some time, not immediately at start-up like in your case...