I almost forgot to say a big thanks to you @Doofus.
I learned a lot from the video post (3 out of 4, the one where they scrape the paint off, then apply thermal grease was the wackiest thing I ever saw)
But the most important thing I learned here was about the 4 wire PWM fans.
My brand new custom built has RGB fans eye candy but unfortunately uses the "old" 3 wire fans. The mobo software include a management suite that among other things, control fans, but it doesn't see any of the 3 chassis fans.Only the CPU fans is controllable, but in 4 increments: Silent, Normal, Turbo and Full Speed.
If my order doesn't get lost in x-mas mayhem, I should receive it tomorrow or tuesday and will report back on temperature improvement.
Thanks again to Doofus and the others !