The best bang-for-the-buck Cinema 4D Workstation currently (10/2016) would consist of the following hardware components:
The Best CPU for Cinema 4D: Intel 4790K or 6700K
Many Cinema 4D features like deformers, generators and cloners are calculated on the processor using only a single-core. This is where you will want the fastest possible single-core speed. The Intel 4790K and 6700K both have 4 GHz and some more Turbo GHz to make the viewport refresh as fast as currently possible. With decent cooling, you could even overclock these.
RAM: 32 Gbyte DDR3/DDR4 (Look for high Clock Speeds, low latency)
RAM is quite cheap nowadays and 32GB helps when you have large scenes and textures.
Graphics Card: Nvidia GTX 1060
There is no need to get an overpriced Nvidia Workstation Graphics Card. Since the bottleneck in viewport speed is almost always the single-core cpu speed, a “Gaming” Graphics Card such as the Nvidia GTX 1060 will be more than enough. This Card can also be used for rendering with GPU-Renderers such as Octane or Vray 3.25 or Redshift 3D.
Mainboard: Asus H97 (Intel 4790K CPU), Asus H170-PRO (Intel 6700K CPU)
HardDrive: Definitely go with the new M.2 formfactor such as the Samsung 950 or 960 Pro. These are blazingly fast. Be sure your Motherboard has a socket.
This Workstation will give you roughly 950 R15 Cinebench Points, which is still very good for rendering. This PC though was configurated as a Workstation and not a render-node, meaning: “As little delay as possible while actively working on Scenes”. If you are looking for fastest render-speed The Processor configuration will have to go into a different direction: Max CPU Cores (e.g. Dual Xeon E5 2630v3), but this will then be much slower for working in the viewport and more expensive!
Check this Link for CPU Single and Multi Cinebench Benchmark Scores of all modern CPUs: http://cbscores.com/index.php?sort=single