Regarding memory.... the latest official info from HP on the ZX00 version 2 workstations in terms of memory is from the latest QuickSpecs for the Z400/Z600/Z800, which ended being published by HP 11/13. The Z800 officially had 16GB sticks of ECC Buffered DDR3 DRAM listed, but the largest the Z600 had listed were 8GB sticks. This does not mean that 16GB sticks won't work. I'd personally choose only the 16GB sticks HP approved for the Z800 if I needed 16GB sticks in our Z600 version 2 workstations.
HP approves specific parts after extensive testing. If they don't test it they don't approve it. That has never meant we cannot do our own testing to prove within reason that something works for us. We do that quite a bit here.....