Di rin may player kasi na malakas sa resources like Total Media Theater i have experience it di fact ang sinasabi ko. I tried some all my 3D ISO lahat may issue naka reformat na nga din ako ng HTPC and latest version na din gamit ko na TMT.
Your GPU load should be the same whether the stream is coming from a BD drive or a ripped BD image, given that you're treating the stream the same way. If you're applying more post-processing on one form than the other because of application optimizations (or the application failing to recognize the stream as something from a BD), then that is not an issue with the hardware.
Now if you're referring to the overhead of managing a loaded disc image, then that would no longer be GPU-related. You may want to change task and/or service priorities related to this to ensure that data comes in on time.
UVD3 (if present and enabled) is a fixed function component of an AMD GPU, so there should be very little variation in performance as long as the software application utilizes it properly. Have you tried checking if ArcSoft's BD & 3D Assistant properly reports hardware decode under Blu-ray 3D?