Firstly, I really appreciate the long post because I'm going through the same thing. I have some conclusion for you.
* 90% of the issues are resolved with a top end CPU.
* All the small adjustments that can be made to enhance fps, most don't work, certainly things like power cables don't work. A better GPU is the easiest best thing for this.
* However, it's an imperfect tech, and you will apparently get drop outs occasionally, it's just part of the deal. I'm not saying it's fine to be this way, it's just how it is and there's nothing we can do to change that right now - it would seem. I've also tried everything suggested on the internet and it's vastly snake oil.
The only thing I can think of is if there is radio interference causing drop outs, though I've tried this in a pretty isolated environment so I have my doubts.
When this works though, it is absolutely worth it. For the moment I can deal with infrequent dropouts (i.e. some sessions are entirely fine, some experience brief drop outs, some experience a disconnect).
I will add though, this mod absolutely reduces temperatures and thus stability.