Try disabling the X entirely and see what happens. It sounds like the graphics drivers are the problem.
Phoronix: Intel Ivy Bridge Borked On FreeBSD, Debian BSD
While Linux hardware drivers still have room for improvement, at least the Linux driver support for recent consumer hardware is still generally better off than FreeBSD...
http://www.phoronix.com/vr.php?view=MTEyNDg
Try disabling the X entirely and see what happens. It sounds like the graphics drivers are the problem.
Am I reading the article wrong or FreeBSD was not actually tested, just PC-BSD and Debian?
PC-BSD is FreeBSD with pretty stuff added on top to make it very easy to use.
Still, when they add the pretty stuff on top they may accidentally break the ugly stuff beneath.