2. HP Z420
If you're after workstation-power for your workforce then the HP Z420 range can offer it in droves. Built around the Intel Xeon E5 processor you benefit from running up to eight cores with 20MB of processor cache for serious computational power in a standard desktop chassis. Using the Intel C602 chipset these systems can support up to 64GB of memory and HP can supply a variety of suitable operating systems including 64-bit Windows 7 Pro to take advantage of that.
With support for PCIe Gen3 HP offer configurations with AMD FirePro 2270 and Nvidia NVS 310 for professional OpenGL acceleration. Powered by an impressive 600w 90 percent efficient power supply unit (PSU) and with an optional liquid cooling system, the PC can stay as cool as it is fast.
Protected as standard with a three-year on-site parts and labour warranty extendible to five, that should give you enough peace of mind when paying out for this type of computing power.