Problem is the EC firmware.  Same issue in the MSI F5.  MSI needs to make an EC to recognize LGA chips and allow bios power limit overrides to work.  Any unrecognized chip by the EC will enforce CPU TDP and ignore what is set in the Bios.

Notebookcheck can bypass this by setting IMON SLOPE=50 and IMON OFFSET negative 31999 in CPU VR Settings in the Bios then they will be able to overclock it to 5 ghz and reach TJMAX :)

The little comparison remarks about other Eurocom models and Clevo are a bit stupid when its clearly not based on a Clevo barebone but an MSI one, like the other 15inch Tornado.

Also, Eurocom does offer GTX 1070 and 1060 (don't remember if they mentioned 1080) on this according to their twitter and an email, but it doesn't show in the configurator at their site so you might have to email in about making that order. You might want to wait for when mobile Turing comes out next year.

Judging by the temperatures (max of 81C in prime?), I would guess that the performance of the 9900K is not being throttled due to thermals but instead by power limitations. Your stress test also indicates this as it doesn't seem to go past the Intel specified 91W.

I am willing to bet you would get better cinebench scores if you up the max core TDP in BIOS to 95 or even 105W. If the BIOS is too buggy, you can even use Throttlestop and change Turbo Power Limits e.g. Turbo Boost Power Max to 105 or even 115W.