As of ~2012, I have used Dell Precision 7000-series workstations for high-end, and the 5000 for mid-range. For the 7000:

CPU: Dual Xeon "2" series (for dual) with maximum speed, then maximum cores. Once you get to 6 or 8 cores, there is little benefit in going to 10 or 12, whereas the higher speed will definitely help. As of 2016, the "2xxxW" series of Zeon processors I think indicate "Workstation" and these are the best choice.

Memory: 128GB is a minimum. I recommend 256GB. For 5D MRS, 512GB is needed. Once the Linux VM's support 128GB, the minimum should go to 256GB, but as of 2016 (VMware Workstation 12) the maximum for the virtual machines is 64GB.

System SSD drive: Most systems (Dell) don't come with the high capacity SSD drives, so I often order with the smallest/cheapest 2.5"SSD as the boot drive, then replace it with a Sansung EVO SSD, which in 2016 is 2TB. Samsung comes with an incredibly easy to use "Data Migration" software that clones to the new drive with 3 clicks. I've used this >10 times with zero problems. You will need a USB 3.0 to SATA connector.

Graphics: Although it's a little more expensive, go for the professional graphics cards (Nvidia Quadro or AMD Pro). Around 2016, I have been using a single Quadro card (supports 3-4 monitors), and selecting the second-from-top of the line. There is no need to get the top of the line as we don't do extensive 3D work.

Monitors: The new standard is 43 inch 4k (Dell P4317Q), which has the same dot pitch (pixel size) as the old 30 inch monitors. I have combined a 43" 4k with the widescreen Dell 34" and that is nice.

Data drives: again, Dell often won't provide the largest drives, so I usually order with the smallest possible 3.5" drive (so the connectors are all set up) and replace it with the largest available SATA drive; choose a fast 7200 rpm drive.

Windows: Windows 10 is fine, and is needed to support memory over 196GB

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