P.J. - I was thinking about your problem a little bit more, this may sound crazy, but have you tried using MadVR as your renderer? Normally it is used for super HQ imaging on high-end machines; however, it gives you a lot of configuration options that can possibly help, such as running the presentation in a separate thread, using Direct3D (well, I think that's only Vista/Windows 7) and lets you control flushing on each of the rendering steps. There are several other settings on top of this....I think I mentioned this earlier, but looking at your screenshots again it seems that the "bad" one shows
very low readings on "GPU Load" and "Memory Controller Load" ...those are the ones associated for the most part with Rendering. ("Video Engine Load" is the reading that has to do with GPU decoding, i.e. what I was rambling on about earlier.)
Another thing you can try (just for troubleshooting) is grabbing GPU Caps Viewer - it's a super-cool tool that lets you see even more of what your graphics drivers are doing than GPU-Z...
CruNcher - Can I guess that you are some sort of software developer/engineer? I am a software engineer and often we deal with "edge cases" (or "boundary cases" etc..) It is almost a way we eventually learn how to think about these sorts of problems (since those are where most defects lie...) I've enjoyed learning from you since I think along similar lines yet do not have your experience level..yet.
