Thanks for your advice. You might be right. Encoding video is an artform.

But I also notice that you are not using 2-pass encoding, so the jury is still out on that.

Anyhow, all that does not change the fact that there's little point in pushing the CPU to decode x265 on a device that needs every ounce of battery life - as your own numbers show.
And certainly you have enough free space on your SD card so that even a 100% increase in size does not matter? Or at least, matters less than draining the battery?
I'm thinking of an out-and-about use case; you seem to be using your Droid 4 at home, probably permanently hooked up to USB charging?