I'm working on a project to soup up the Z400, and have some results. Mine came with a W3565 quad core processor, and I read in our forum here that this "revision 1" motherboard with the later boot block date (11/10/09, from BIOS) and the 6 memory slots can support running a X5690 processor despite the fact that processor was never listed in any of the HP QuickSpecs for this workstation. That processor is equipped for running in a two-processor workstation (it has 2 QPI links rather than just 1). It also is said to be the fastest processor that will run in a Z600 outfitted with two processors (that would use their two QPI links each, and it also was never listed in the HP QuickSpecs for the Z600 "revision 1" later generation motherboards). It was listed by HP for use in the "revision 1" Z800.
I can confirm that the X5690 runs just fine in my "revision 1" Z400, and have some advice on a less expensive eBay used processor that should give the exact same performance.
Some Z400 generalizations: Most of them came with the higher capacity "Performance" 463981-001 heatsink/fans that can handle the 130W max TDP processors. These are larger, have 92x92x25 mm fans, and have 3 instead of 2 heat tubes built in. Because the Z400 is a single processor workstation it is optimal to use a hexacore (6 cores) processor. You want the fastest available processor clock speed that will run in that workstation (3.46 GHz), and you want the highest transport speed (6.4 GT/s QPI). You want the largest cache (12MB SmartCache). You want the FSB of the processor to be the highest possible so that if you have fast memory it will be allowed to run at its fastest speed and not held back by a slower FSB processor (you want 1333 FSB for this). You also would prefer a Xeon with only one sSpec code so you don't have to figure out what version is the latest.... there will be only 1 version if there is only 1 production sSpec code. Never buy one that has a sSpec code that starts with a Q..... it will be a "Qualification" pre-release processor. Prefer to buy from a US rather than China source unless there is a great deal from a proven good source, and you don't mind waiting 2-3 weeks.
Update to the latest BIOS, which is 3.60 and came out 4/16. It is best to use matched memory..... six sticks of either 2GB/stick or 4GB/stick with each stick having a speed of 1333 to match the fast FSB value of the processor... that gets you fastest memory performance with matched channels.
The X5690 (with a single sSpec code of SLBVX) sells used on eBay right now about 220.00 USD. The equivalent single QPI link processor that is in the latest HP QuickSpecs document (v54) is the W3690 (with sSpec code SLBW2) and it sells used on eBay now for about 170.00 USD. So, buying that will save you about 50.00 over the X5690 for the same performance, but you won't be able to shift that over to a two-processor Z600 setup later. Here's some stats for the three processors discussed above:
W3565 Xeon 3.20 GHz SLBEV 130W max TDP 4 cores 4.8 GT/s QPI 8 MB SmartCache 1066FSB 25.00 eBay
X5690 Xeon 3.46 GHz SLBVX 130W max TDP 6 cores 6.4 GT/s QPI 12MB SmartCache 1333FSB 220.00 eBay
W3690 Xeon 3.46 GHz SLBW2 130W max TDP 6 cores 6.4 GT/s QPI 12MB SmartCache 1333FSB 170.00 eBay
The W7 performance scores below are from the same Z400 before and after the processor upgrade this morning, and the video card scores shown will rise when I put in a faster GTX or Quadro card. I tend to stick with the Intel 320 series SSDs off eBay because they are SATA generation II SSDs and have been rock solid for me. I like the 300GB version best, which often will give me a 7.8 drive score. The maximum score for any subcategory shown is 7.9.
Here's a W7Pro64 Windows Experience Index probe for my original processor. Note that the processor and memory performance into here is the thing to focus on. This is the fastest latest quad core released for the Z400. The switch to a faster video card will raise the overall score, which is based on the slowest component in the speed test:
Here's the same for the X5690, and the W3690 will produce the same scores. This shows the benefit of the faster processor and the higher number of cores used (6 versus 4). Again, dropping in a fast GTX video card will raise the 2D and 3D video scores up to about 7.8:
