Here is Epic’s workstation specs:
https://wiki.unrealengine/Recommended_Hardware#Building_a_Computer_for_Development
If you are considering building a powerful machine for UE4 development for around $2500, here is a spec we recommend:
Intel Core i7 4930K processor
Intel X79 chipset motherboard
32GB RAM
1TB SSD
Nvidia GTX 770 video card
Of course, now you would get a 980 or Titan X. 