There are some added things to be aware of. Some of these PCIe M.2 SSD drives do have amazing speed potential, assuming you also have amazing speed potential on your PCIe bus. Take, for example, the 6 series HP workstations:
The xw6400 had only PCIe Gen 1 slots (plus a few legacy PCI slots). Then came the xw6600 with its two PCIe Gen 2 slots (the two video slots). That is why I put my HP Texas Instruments based PCIe "2x2" USB3 card into the second of those two slots..... its USB3 bandwidth can be matched by that PCIe Gen 2 slot. That also would be where one should put a PCIe SATA III card in a xw6600, because the other non-video slots are all PCIe Gen 1.
You get where I'm going..... the Predator card, on the Kingston web site has "Interface: PCIe Gen 2.0 x 4". But that does not matter for those of us with the ZX00 series of HP workstations because all the PCIe slots in those are Gen 2.0 or Gen 1.0 too. You can look in the technical manual to see which is which. Surely don't put it in a PCIe Gen 1 slot...
Rough data: a M.2 Gen 3.0 PCIe SSD in a Gen 3.0 PCIe slot may reach 32GB/s; in a Gen 2.0 PCIe slot it may reach only about 10GB/s, and the SATA Gen III 2.5" form factor in a SATA Gen III workstation may reach 6GB/s. The ZX20 workstations have some SATA Gen III, but the ZX00 workstations are SATA Gen II, by the way. So, don't expect the ZX40 PCIe Gen 3.0 slot speeds from any of these PCIe SSDs in your Z400. However, you still can expect a boost from this project.