We're doing things that HP did not intend, and yet they don't pull the plug on us helping each other.
The key info to search for is the two boot block dates, and if you have the earlier one then you are limited to the older processors. The "microcode" thing has to do with HP having a "white list" built into BIOS that checks to make sure the processor(s) present match one in that list. When you try one that does not match it is a flat no-go.
I jumped mainly from the xw6600 to the Z620 workstations, so I have not experimented as much with the Z600 workstations, but they are excellent. I am sure that if you choose to stick with your original motherboard you will be able to find the fastest processor HP ever certified for it, and will benefit.
HP does have a QuickSpecs archive you can search through. Make a list.... you'll see what they started with, then added to, and finally you'll see the "revision 1" box show up with the newer type processors. As things go forward you can even see some processors drop off the list, but I have never found that a "dropped" processor will not work with one of the newer BIOS versions. The microcode updates are generally included with BIOS updates, but they can be released a a microcode-only update (rare). So, the advice is to always use the latest BIOS if you are doing these type of upgrades.
Keep us posted!
p.s. Oh... and HP has a confusing AS# and SP# for parts.... two for the exact same part. One assembly, and the other spares. So, you need a decoder ring too.
