Thanks for all your help.
729 motherboard arrived and two 5160 CPUs. 729 M/B also has a processor on it...5130 I think?
Anyway, I installed the two 5160's on the existing M/B and installed Win7 64bit Pro. Mostly generic drivers and I followed your advice in another post about (I think) the Z620 drivers being usable? HP had the full set of drivers in one package so I downloaded and ran it with the files all automatically going into a folder C:\SWSetup\SP68644.
From there I went down the list in device manager, right-click, update driver, (after pointing to the folder once it remembers the path), and installed anything that would update. So far, so good. Will run a stress test soon.
I still need to get a Win7 license and I think I'll try a different video card. I had a Radeon 8400 which is fine but I am sure I can find something to jump up the graphics a bit. I don't care to get edgy as I am trying to keep costs down.
I plan on installing the 729 M/B with the two 5345 CPUs just to see if I can get those working, then I may get another 6400...maybe. Still have the other 2 x 4GB memory as well.
Right now I have a 320GB hard drive but may install an SSD as you mentioned and use the 320 as secondary/backup. I did see some Samsung Evo's at a good price and will watch out for the Intel's as well.
Once again, appreciate your help and all the other posts you have on this subject...very helpful.