I also only use windowed fullscreen mode 2560 x 1080, as fullscreen mode crashes the game often. I get stuttering during the game only when I'm airplaying (mirroring the screen) to my AppleTV, and it can crash the game doing this, as this puts additional stress on the system, but I'm surprised how well this works. I get frequent crashing during the loading screen.
The FPS drops often occur when leaving the lobby, and sometimes in the battle bus (which is usually around 60fps).
My experience with Fortnite is that during gameplay, it rarely stutters, with most settings on EPIC, with AA and shadows set to high. Building a CustoMac Hackintosh: Buyer's Guide
