Windows And Mac Recommendations
Prosumer (or midrange)
Professional (or high-end)
Keep in mind that the CPU recommendations are valid until Intel introduces a next-gen architecture. If you want redundancy as well as speed from the RAID array, double the number of drives. The high-end system's GeForce GTX Titan is essentially a lower-priced substitution for a Tesla K20, which you're welcome to use if you have the means. If you are going to be working on feature-length projects in 12-bit 4K, expect to need more drive space than mentioned above.
Here, the hardware options are a bit more limited, since most current Mac models are dependent on external connections for additional storage. If you prefer LaCie over G-Technology, there are equivalent products to the ones suggested above. If you don't like the iMac monitors, or want to go with a 30-bit display, you can always use a Mac Mini.