Well, you just have to test it for yourself to see what you like.
I did a quick test for you to perhaps give you a starting point:
Source is uncompressed Tears of Steel 1080p.
Base command line is x264 --preset veryslow --tune film --level 4.1
"Without b-frames" is with added --bframes 0.
"Pbratio 1" is with --pbratio 1.0 --no-mbtree.
"+10%" is with 10% bitrate added.
As you see the differences aren't that big, and without b-frames might even be better than with big b-frames and without mbtree.