I know the feeling, I made this account specifically to braindump what I’ve been able to figure out so far. If you find something interesting or informing just be sure to add it to the borg collective I mean thread.
The most helpful thing I’ve read/watched is the POWER9 presentation in January 2017 by Jeff Stuecheli given to the AIX Virtual User Group, the video is available for download (something went wrong with their YouTube uploads), and the slides are available as a PDF. If you want to skim it, I have timemarkers in a post from the previous thread.
The image about POWER9 Processor Family that I posted earlier is a slide from that presentation.
Something I noticed when trying to export the slide as an image, the PDF is horribly screwed up in places; some of the images (the Power Systems logo for example) were exported as horizontal strips. So instead of one image, the PDF stores 100+ images that are 1px tall. If you are wondering what I mean, try opening up PDF in Inkscape and you’ll see.