can CPU be drop-replaced in a Z4 G4? is overclocking possible?

[DanRdz]

Hi, I am thinking of buying a second hand but with 2023 warranty, HP Z4 G4 with a 7900x and no graphics. I have no experience with HP workstations. so apologies if naive questions 1) can I later on replace the CPU with anyone offered in the non-Xeon lineup for this model or is BIOS locked somehow as to prevent CPU replacements? 2) in a YouTube video I saw, it says that only the Xeon model can accept the PCIE 4x4 NVME adapter from HP, does this mean I cannot use a third party 4x4 NVME PCIE adapter card (I currently use one from Asus on a self-built X399 system, 3) the 7900x is unlocked of course, does HP bios allow any overclocking or is it Locked by BIOS?

[DGroves]

OEM business and most definitely workstations do not support overclocking,....this is due to the fact that workstations value 24/7 operation and stability quite highly

the HP Z4 G4 line has TWO DIFFERENT SYSTEMS (i7/xeon cpu's) each using a different motherboard and slightly different options for each

each system only  officially supports the listed cpu's however intel may release a newer cpu in each cpu family at a later date that HP may not test and list that might work

the HP quickspecs lists each system and the differences between each line,...

https://www8.hp.com/h20195/v2/GetDocument.aspx?docname=c05527757

only the xeon one supports Two m.2 ssd slots on the motherboard

any generic m.2 pci-e card will work in both systems

[DanRdz]

Many thanks for the useful answer. do you know if there is a decibel rating for this machine under load? that is what is the noise level of the machine with fans 100%? (asking as I am more used to liquid cooling, and less with air cooling as this systems seem to have).

[DGroves]

under normal conditions the fan(s) will never ramp up to 100%

you would have to be in a environment that is over 130 fahrenheit for this to happen

again,...............READ the quickspecs as they list the systems temp range 

[DanRdz]

Thanks I will read it carefully specially any info on the TDP rating of HP cooling solution. As a matter of general logic for me, if the fan is never at 100%, there is CPU performance being left on the table under heavy sustained loads. I can appreciate people preferring quieter machines (me included) but as fashionably re-lebaled lately as Intel Thermal Velocity Room, any modern CPU should take all space allowed by the cooling when it is demanded to perform. 

[DGroves]

you are confusing the case fans with the cpu fans both operate off different sensors

you will never get both at 100% in normal usage

in general the cpu fans will ramp up down in speed depending on utilization

the case fans will only ramp up if the internal air temp starts getting to high

no computer/case designer wants their system to go to 100% fan usage as that means the system will cpu throttle quite early if the outside ambient air is warmer than what they tested for