Also known as MacPro6,1.

My Mac Pro is the middle tier has the following specs out-of-the-box:

• CPU: Intel Xeon E5 3.5GHz 6-Core with 12MB L3 cache and Turbo Boost up to 3.9GHz
  • It is not soldered, so can be replaced by other CPUs from the same family.
• GPU: Dual AMD FirePro D500 graphics processors with 3GB of GDDR5 VRAM each
• Memory: 16 GB of 1866MHz DDR3 ECC RAM
  • Maximum 64 GB is supported according to Apple. Apparently up to 128 GB is the actual limit, but will lower memory speed.
  • You can not mix buffered and unbuffered memory.
• Storage: 256 GB PCIe-based SSD.
  • It has a proprietary connector, the same as used in the MacBook Pro 2015. With adapters, regular M.2 SSDs can be used.
• Power: According to Apple, power usage is between 43 W (idle) and 238 W (max load).

• https://support.apple.com/kb/sp697?locale=en_US
• https://support.apple.com/en-us/102839