That's correct for both.
Stock images are trusted by the trusted boot module that determines whether to trip Knox or not.
And as the images do not contain a user data image, user data is retained. Still, it wouldn't hurt to backup your important stuff anyway. I did this the other week, and expected to have to set up my phone again. But when it turned on, it was as if I hadn't done anything but I had, as root was gone (which was installed to /system).
@techfanatic can you please add the Canadian 920W8 OE1 build as well?
Can I flash XEU firmware with odin to my network locked model? I'm on EE and would like to have the unlocked unbranded version on my device?
XEU version http://www.sammobile.com/firmwares/d.../SM-G920F/XEU/