When debugging this problem:
I also had another one: the above configuration, which works fine both for new and old Xorg releases and both for x86_64-256.35 and x86_64-195.36.24-pkg2, will hang the machine when an unused video card is present.
I have a GTK275 in the lowest PCIe slot. When a 7300 is also present, in an upper slot, then starting X11 with either of those drivers will lead to a blank screen, no reaction to keyboard presses and no network reactions. In a word, a hang. The keyboard LEDs are not blinking which would mean it is not a panic but it is also possible that the kernel tries to blink them and X11 has hijacked them already. Removing the 7300 fixes the problem. Xorg -keeptty showed the same behavior, same blank screen, no LED activity.
Xorg.log and config file from when only one card is present are here (same as other thread).
I only have an Xorg.log with both cards when I run Xorg-7.1.1. Apparently that worked better than the new Xorg. The problem is somewhat intermittent, although the new Xorg reliably did this every time today.