Encoding High@L3.1 for Playstation Vita

[verifonix]

I was trying to get x264 to encode H264 video for my Playstation Vita. I was surprised there wasn't as much information on the matter as I'd expect.
After some hours of getting "This file is not compatible" errors on the handheld, I figured I might as well break down what was the problem.

Edit: after some confusion, it seems things actually changed along with firmware.

Prior to 2.00 files were checked to be of High@L3.1 specifications, 720p files can play (downscaled)

After 2.00 files can be up to High@L4.1 specifications, 1080p files can play (downscaled)
B-pyramid works, and it doesn't look like you need to set any maxrate/bufsize.