Everything is fine. Different cores finish at different times, it's just how modern CPUs and OSs work. Don't forget the CPU is still doing other stuff within the OS itself, which accounts for some of the difference. Then there's minute differences between the cores, boost speeds, all sorts of things. All is good, basically
Loading your system with a synthetic benchmark is NOT a good way to check for gaming stability when it comes to graphics cards. If you've overclocked your GPU, reduce the clocks and see if the error still occurs.
^This. Possibly uninstall / reinstall drivers too. I did a quick google and a suggestion was that that error could be to do with PhysX - try either disabling that within WoW or reinstalling and making sure that PhysX installs correctly.
I get the video scheduler error when things are pushed that little bit too far. If it is at stock, then perhaps you've got issues elsewhere. Like George said, I'd suggest reinstalling drivers to be safe.
