Go with 32gb ram, clock speed is a lot less relevant than people thing, just make sure to get CAS latency 9 or bellow, that’s what really makes a difference. I always go with Corsair or Kingston for ram. A Decent graphics card like GTX 970 or 980 (both will handle UE great and you won’t really see much of a benefit in UE with 980 unless you plan on developing games that completely require a card like that. I usually go with Asus but the Gigabyte G1 version have steadily outperformed Asus’ Strix version in the latest cards so I went with Gigabyte this time.
For a CPU go with Intel 4930K or 5930K depending on which socket you want. I’ve heard they use the 4930k at Epic and I use it as well, works great and compile shaders very fast compared to my old quad core i7.
A fairly big SSD is important, 250-500gb, I would suggest Samsung (go with their EVO versions, pro is a waste of money), otherwise Corsair or Intel. OS takes tons of space (~30gb for 64 bit win 7 and ~20 for 64bit Win 8.1), then you’ll get filled up with appdata, also lots of softwares (zbrush for example) won’t let you choose which drive to store temp files on, so having a small C: drive is awful. I use one 500gb Samsung Evo 850 and one 250gb Samsung Evo 840 at the moment.
Then just plonk in a strong enough PSU, I’d say go with 800w so you have room for two GPU if you want to go SLi some day. I prefer Corsair’s PSUs.
Lastly, just fine a motherboard that supports the socket you went with and have room for however many RAM modules you choose. I usually go with ASUS and then find a case that can fit your monster hardware, I like Corsair’s cases.
Might want to pick up a regular harddrive for storage as well, go with Western Digital or Seagate.
This is of course over the top and not at all what’s required, but if you have a big budget to spend, it will definitely be worth it and will perform great in both game development and playing games.