Nelson..... may I recommend that you contact the poster on the thread below, who wrote 10/2/15 about getting the X5690 plus 48GB of RAM going on his multiple Z400 workstations? That post is the one that finally convinced me to go ahead and buy my first X5690 for my Version 2 Z400 workstations (the ones with 6 memory slots instead of 4).
The link is HERE.
It would be very valuable to find out from him exactly the brand and source and ordering code for his 8GB sticks which are proven to work in his multiple Z400s. Once you have one of those sticks in hand you can sometimes locate the exact same thing used on eBay from the codes on the label attached to the stick. If he would scan in a front image of one of those sticks with its sticker visible that would great, too.
Please keep us posted on this project, and good luck!
Scott
