Memory Upgrade for HP z420

[ryanm]

I have an HP z420 with a Xeon E5-1620 v1.

I would like to upgrade the memory. It currently has:
DIMM1: 2GB
DIMM2: 4GB
DIMM3: 2GB
DIMM4: (empty)
DIMM5: (empty)
DIMM6: 2GB
DIMM7: 4GB
DIMM8: 2GB

I would like to upgrade to 32GB. At first I thought I should just buy 2 x 8GB sticks. However, based on how I read HP Z420 Memory Configurations and Optimization, it looks like I am probably not taking advantage of channels appropriately and 2 x 8GB would not be optimal.

If I were to upgrade the memory, is my best bet to try and buy 6 x 4GB and replace the 2GB sticks and w/ 4GB and fill the 2 empty slots?

Other than matching Un-Buffered ECC and speed of 1600mhz, do I need to pay attention to anything else when shopping for memory on eBay?

 

[neb50]

You could probably get 4 8GB sticks of Reg. ECC memory cheaper and replace everything that is in there now. I don't think you can mix ECC and non-ECC so you will need to use one or the other.

Also, since that processor only supports up to 1600mhz, Ebay has some sets for under $60 shipped.

 

[Spartacus]

I'm pretty sure I have a swathe of 4gb r-dimm cant remember if they're 10600R or 12800R, but you could have them for a case of beer and the shipping pretty much (like $20-25).

That said I also have 6x 8gb DDR3L 12800E sticks that I think....are skhyinx that should work.
I'd have to check the going rate but iirc they arent cheap, like 2-3x the rdimm modules.