Just for the records a few information:
Yesterday, I've bought a
KT3 (G000 K905 xxxx xxxx) in Germany in the current winter sale action (49,- €). It came with the miraculous firmware 5.8.9.0.1 (3175970011).
Kept it from the software point of view completely untouched, i.e. I just took it out of the box, selected the language, skipped the WiFi setup (airplane mode), but did
not register it with Amazon and also did no factory reset. I was perfectly able to begin the procedure from post #1 with
step 4, i.e. UYK with the initial factory build 5.8.0 stored in the root of the user drive. In step 6, I used the latest "nomax" hotfix build (which I believe is the very best for all users; it should be linked in post #1 as default).
In step 7 my friend (I bought the device on his behalf, and just helped him with the jb because he is definitely no computer nerd...) decided to use the latest KT3 firmware 5.8.11 with his now jailbroken device, as he is very interested in the new boldness and font size scaling options. He knows that there will possibly be problems when hitting the "Reset" button, but he promised to be cautious.

Everything went fine. Hotfix did its job, jb survived.
And a piece of "nice to know" info, as this is discussed here often:
Both the booklets
and the kindlets for KUAL and Vlasoftsoft's launcher etc. still work with the jailbroken 5.8.11, though the KT3 is an 8th genertion Kindle.
Given this experience, I decided for myself finally to upgrade both my jailbroken KT3 and PW3 to 5.8.11 now, though I have - yes really! - only one single AZW3 book on my Kindles (and this is the Amazon Users Guide), thus there is no real need for the new features that only work on AZW3 and KF8 format. (BTW: I'm definitely a customer, Amazon hates, as I have never bought a single book from them - just using their Kindles as a perfect and reliable hardware platform to read PD classics and DRM-free MOBIs from other sources.

My Amazon account is used only for testing purposes.

)
Hope, this info might be of interest for some of you.