I recently got an 5K iMac (El Cap 10.11.5, late 2015, intel core i5 3.2GHz, 8Gigs ram, AMD Radeon R9 M380) and tried to use the unreal editor. When I create a new project, it loads until 96% and then the loading screen disappears and my iMac freezes completely. I tried using different configurations, and even using 4.11.2 but none of it seems to work. Pd(Once it opened but the editor crashed as soon as I selected the sculpt option)
This might be pertinent