Im running :
2600K 4.0ghz
GTX 670 1200mhz core 6500 clock
32GB g skill 1866mhz ram
750 watt psu
SSD sata 2
^ runs UE4 really nicely in most cases (depends on how your using gpu particles along with high res meshes IE super ultra graphics vs just good graphics)
EDIT: there have been a few guys running cards like the GTX 650 and a GTX 465 for instance and have had averages of around 15-45 FPS, so really you want a GTX 670 or higher form nvidia, apparently AMD 7800 series 2GB cards get 60 FPS in UE4, as I dont own anything AMD I can’t say how well it really runs, these benchmarks were for heavy graphical levels also, so take it as you will.