Alright, I'd do the xeon because it is a i7 without GPU, and will help more in AutoCAD. I'm not much on the workstation GPU's, and thankfully you already have them. I put a 750watt gold since it's total overkill after looking at the power consumption. Atleast, that's the Nvidia site. Xeons don't OC, so H97 is good for this. SSD for OS and a large HDD for the files. The prodigy is small and is perfect for this. I did not put an OS.
PCPartPicker part list:
http://pcpartpicker.com/p/TLzpQ7
Price breakdown by merchant: http://pcpartpicker.com/p/TLzpQ7/by_merchant/
CPU: Intel Xeon E3-1231 V3 3.4GHz Quad-Core Processor ($273.22 @ Amazon)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($27.78 @ Newegg)
Motherboard: Asus H97M-PLUS Micro ATX LGA1150 Motherboard ($113.38 @ Amazon)
Memory: PNY XLR8 16GB (2 x 8GB) DDR3-1600 Memory ($149.99 @ Best Buy)
Storage: Crucial MX100 256GB 2.5" Solid State Drive ($109.99 @ TigerDirect)
Storage: Seagate Barracuda 2TB 3.5" 7200RPM Internal Hard Drive ($83.99 @ Best Buy)
Case: BitFenix Prodigy M Midnight MicroATX Mini Tower Case ($99.99 @ TigerDirect)
Power Supply: SeaSonic G-750 750W 80+ Gold Certified Semi-Modular ATX Power Supply ($110.29 @ Newegg)
Total: $968.63
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2014-08-16 00:13 EDT-0400
***I put in the newer version of the CPU you mentioned.***