The 971H has 2 major advantages, 1) Genesis/Faroudja chipset 2) DCDi by Faroudja (side effect of using the chipset)
It seems the 971H was made with the intent of being an exceptional video player. Period. The 970HD has more feature but the video section is of generic quality. Meaining it will not do as well as the former in video tests. What is to be seen is how much worse is the performance...
I believe this should be how to explain the difference,
971H - Superlative for Movies and average performance for all else, if available
970HD - Average performance for all capabilities, if available.