Here's my quick tests:
http://pastie.org/569295
http://imk.cx/temp/dead_space_mbtree0.mkv (13,94 MB)
http://imk.cx/temp/dead_space_mbtree1.mkv (13,95 MB)
SSIM
0.9728932 -> 0.9740763
Here's two comparison shots:
Dark_Shikari let me know that single frame comparisons are useless for ratecontrol comparisons, but with the above shot, you can see that it brings out some more detail in the darker areas.