Ok, thank you. This confirm what I wrote above:
"What I know for sure is the Bus ID for the 1st card (HP subvendor) is 4, while the other two NVS300s are 7 ad 8 bus ID#."
Now, again, I will try address myself the question referring to the above scheme:
"Is PCIE1 slot linked Bus ID4, PCIE3 to 7 and PCIE4 to bus 8?" Again, I can't stop fans that do not exist as workaround.
Then will post the topic of my question in a proper thread (one of those 3 cards is systematically lazy on clock, even if the temperature is low)