DGroves... Happy to help... HP never updated a bunch of its documentation for the Z400/Z600/Z800 when the motherboards were updated from version 1 to v2. Those DDR Quickspecs links, however, reflected the version 2 ZX00 workstations but they had been missing in action for years. I was lucky to find a HP source for them that works again!
To the OP..... the 8GB sticks I tested in my Z600 v2 have an even faster maximum MHz rating (1866) than what you post about. The workstation's memory controller is designed to down-regulate automatically to match fast MHz memory down to that of the processor. Mine are single rank sticks, and yours are dual rank but that should be fine if all 6 are identical. You never know if non-HP memory will work unless you test it out. The ones I'm using are Samsung, but SKHynix is also excellent memory. Here's a pic from the SHKynix link you provided showing your -PB memory can run all the way down to 800MHz:
The HP Z600 drivers web site has a "Diagnostics" section that includes two "HP Vision Diagnostics" packages, for making either a larger diagnostics USB drive or a smaller CD-ROM drive. The memory diagnostics on both of those is the same.... and excellent. I always run that when I do these type of experiments, and there were zero issues found with the server memory I tested. I had it run for about 4 hours total....