Love all the surprised posts on that thread in spirit of "Will it really work...but what's the catch ?" :- )
Also 75Celsius is not a lot...these pedenatic people. Nonetheless, I too have under 55 because of good workflow and cooling for my 2680v2 (Fractal XL and 2xNoctua U12S does wonders even in horizontal push which I prefer for silence),
but it absolutely is not needed.
That full HP refurbished is OK deal too :- ) I mean it's hard to find 2x those CPU plus board for much too much less anyway and you already get some memory, PSU and case as well. Just don't forget to swap the fans (not heatsinks ! just fans for Noctua), to keep it quite, HP uses incredibly cheap shit, and they're also been used for long time, their bearing mostly gone south.