Major Judder Problems, OpenGL

I'm running Windows 8.1 x64, GeForce 780 ti. When I run the Oculus World demo how it is normally built it is wonderful :D

I modified Platform_Default.h to have this:

  #define OVR_DEFAULT_RENDER_DEVICE_SET															\
        SetupGraphicsDeviceSet("GL", &OVR::Render::GL::Win32::RenderDevice::CreateDevice)

to force the demo to use OpenGL rather than DX. Configured as so, it crashes if opening in Direct Mode (somewhere inside EndFrame). If I run it in extended mode, it no longer crashes, but I have extreme judder. No longer buttery smooth and convincing, it's more like head tracking is running a frame behind despite the game running at 75fps.

It's not so much that I want to walk around Tuscany using OpenGL, but my own game is having the same exact issue (and it's OpenGL only currently, I can't just toggle a flag unfortunately). I wanted to confirm whether my own game was broken, or whether it was a general problem, and it appears to be a general problem.

Is OpenGL nearly completely broken in conjunction with the 0.4 SDK and Windows 8.1? I can live without Direct Mode, but the judder is unbearable.

EDIT: I am not a clever man. I misunderstood what setting the Oculus as the primary display meant. After checking the "Use as Main Display" checkbox the judder is gone!