I have to say, the Open World Kite Demo is pretty amazing.
The only issue I noticed was when moving between levels quickly (UAV with Shift held), at which point I found it stuttering while unloading and loading assets.
But then again, this was running in the editor.
Memory with everything loaded was just shy of 20GB, though my system generally runs at 3.5GB used (a few other programs running in the background while playing with the Kite Demo).
I expect that if I was playing with the release version, the memory wouldn’t be as large and things might load faster.
System Specs: i7-5820K OCed to 4.4GHz (6 cores, 12 threads), NVIDIA GTX 980, 32GB DDR4 @ 2133MHz, Assets loading from a 4 x 256GB SSD in a RAID 0 configuration.
Once again, Props to the UE4 development team for this amazing demo and the engine that runs it.