A few clarifications:
1. DGroves accidentally mixed-up info on the Z4 G4 with the Z8 G4. It is the Z4 G4 that has two physically different motherboards, one officially for the Xeon and the other officially for the Core Intel processors. Neither of those Z4 G4 motherboards can run Optane memory. Both can run the Optane SSDs that HP lists in their QuickSpec documents.
2. Faster memory cannot make a slower processor run faster. Your processor is rated by Intel to max out at 2933. I think it would be a good idea to get two more memory sticks identical to what you currently have, rather than Optane memory.
3. There is a good HP White Paper document on Optane memory use in the Z6 G4 & Z8 G4 (referenced in the Z8 G4 QuickSpecs under the Optane memory section) that does not link properly and can be hard to find... A copy is attached below as a PDF for reference, but I agree technology has moved on from that.
4. By the way... quality M.2 NVMe4 SSDs run faster in the ZX G4 generation of workstations despite the PCIe slot technology in those topping out at NVMe3. Same thing for the ZX40 family of HP workstations. That's what I'd recommend investing in too if you're not already running good NVMe3 M.2 SSD(s). I have not tested a NVMe5 M.2 SSD in those yet.
See attachment...