liprsyme: Yes, I should have mentioned it, but the texture I'm using for the floor plane is just a 1 x 1 pixel white texture that's just tiled over the entire thing. The texture's format is X8R8G8B8, but I also tried just a few moments ago changing that to A16G16B16R16F just to see if it would help. It did not.
AgentC: Interesting. What about the fact that the bands are still there when using the DXGI_FORMAT_R16G16B16A16_FLOAT back buffer format? I've posted a picture. Please disregard the non-gamma-correctedness of it (it's automatically put into linear color space, see here http://msdn.microsoft.com/en-us/library/windows/desktop/ff471325(v=vs.85).aspx). At this point, is it basically just the fact that the monitor is incapable of producing a colors between those banded values? By the way, you're right - the image is produced identically when I switch to the forward renderer.
powly k: That's a good idea, I may try that out if it turns out to be strictly a monitor-related issue.
Editted to include image and forward rendering comment.