Depth of Field fullscreen performance issue

Hi,

I'm using the depth of field shader in the editor at a resolution of 800x600 and it runs fine, I get upwards of 100 fps. However, running the same scene with the shader in a standalone release build (either fullscreen or windowed) at 800x600 yields very low frame rates, < 10 fps. Why is this?

EDIT: One other really weird thing. Right, if I remove the depth of field component from the camera and then run a release build, it'll run at a very high frame rate. However - if I leave the depth of field component attached to the camera, and then attempt to disable it (by doing GetComponent().enabled = false), although the depth of field is no longer visible it still runs at a ridiculously low FPS. This also applies to using Destroy(GetComponent()). Also, changing resolutions/other graphics settings appears to have no affect at all. Any ideas?