This two X5650 will be fine for me. I might upgrade to faster CPU's next year, but for all my current needs this is perfect.
I don't have any intention to use Quadro GPU- I will use my GTX 660 and later upgrade to GTX 1060 when I switch from my multi monitor setup to single 42" 4K TV.
Win 7 and stock HDD's will not be used. I have 120 GB Kingston Fury SSD for OS and apps and 2 TB WD Blue for storage.
I will use Windows 10 Education which is the same as Enterprise version but without Cortana (which I don't need).
USB3.0 will be used-thank you for recommendation. DVD drive is junk for me since I don't use optical discs since 2010. Can Z600 boot without DVD drive? I really want to replace it with drive bay with card reader and couple of USB 3.0 ports for the front.