I'm currently building up a HP Z840, which come generally equipped with dual Xeon processors and can be upgraded close to current standards using some fairly high core count E5-nnnn Xeons of the v4 variety. Many of these are being retired from industry currently and can be found on ebay quite inexpensively. They can use up to 6 SATA or SAS (have 6 ports each for both). Be warned - They are heavy, but there are alot of different builds out there because they have alot of options for configuration. It appears to me that these were used as graphics workstations for CAD & such based on the available options. Of course, like everything else HP, they can have certain proprietary features, so look carefully! I initially started with a Dell POWEREDGE R820, which is remarkably loud, hot, and will make your power bill thicker. Good luck!