My CPU has been very busy lately, reencoding the same episode of 1 Litre of Tears over and over again to find better tweaks (and now it's reencoding Densha Otoko). In general, it seems that very small gains can be made from tweaking x264's settings, and the biggest gains are to be made in noise reduction and crf targets. Although I upped the crf from 24 to 23 to get better quality and less macroblocking in certain scenes (especially 12:17 in the 1st episode of 1 Litre of Tears, where there's quite a bit of mosquito noise and slight visible macroblocking). Unexpectedly, reducing the frame rate did not make the videos smaller.
Here's the raw data. Original means:
3 bframes, 3 reframes, no open gop, merange 24, motion estimation: umh, subme: 8, crf 24, tuning: film, Main Profile, 3.1, nr:200. Apparently I really shouldn't use tune: film with JDrama shows.
Sadly the minuscule gains in file size were obliterated when I upped the crf to 23. There is no substitute for more bandwidth/data when it comes to improving quality! The filesize/length of show ratio still stands at 100MB per 23 minutes. That works out to around 230MB maximum for the first episode of 1 Litre of Tears, which is 52 minutes long. Current encodes, which resize the video down to 704x400, are well below that mark, so there's room to grow. 848x480 provides a marginal quality improvement, and balloons the file size to around that 230MB mark. I don't think it's worth it.