This is the only thing I was refering to.
And if you do a proper 2-pass encoding of x264 you can tweak it so that it's just as good as x265, while being maybe 25% larger in filesize.
- But it makes a huge difference during playback (CPU usage).

I did actually do this once, let's see...

Here's the script I wrote, takes a while to get into it, but then it compares x264/x265 pretty straightforwardly:
(script deleted because it is known to suck, and not the point of this discussion)