END OF DAY REPORT:
1. my CPU is now overclocked at 4.6Ghz.
2. My GPU si now further overclocked, but not by much.
3. I have played with all settings I have found on steamVR and Windows Mixed Reality.
4. MAIN_T is a tricky parameter. What I know is that when I am in single, it runs around 97%, but fps is stable at 90 (though not every single time, as sometime I need to start the game twice... go figure). So, yes, it is high... but maybe that's not much the point.
At this point I am very confused as for what to do. I could try to overclock the RAM, but none of you suggested it. On the other hand, it is quite unclear that an upgrade in GPU would straightforwardly solve the problem. right?
All in all, the main lesson again is that the XGN community is really amazing. Did we solve the problem? No. Did you make me feel like I have amazing friends who are there to help me. Yes. Very much.