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
The 4930K is a great cost / CPU power trade-off for compiling the engine and running the editor.
We have found SSDs to be the best user experience, and with the advent of the Samsung Evo series even large amounts of SSD storage have become attainable.
Copious amounts of RAM is the single biggest contributor to a smooth user experience. While the editor and engine don’t use 32 GByte, having the memory available for the disk cache is a boon, especially as a programmer compiling the full engine. We found going above 32 GByte resulting in diminishing returns.
You can take the consideration of Evols along with this list and shop around for what you can afford.