I'm on the fence whether to get a flashed card or not.
I purchased a GTX 1080 ti primarily for Windows gaming, but tossed it in my Mac Pro 4,1 (updated with 5,1 firmware and Sierra) once I saw a driver was available. I don't know if it's just me, but I'm barely hitting 54 FPS with Valley, and 62 FPS on Heaven benchmarks at 2k resolution. Sorry, it's the biggest monitor I've got, so can't test 4k and higher. I'm sorry to say Borderlands 2 still has a lot of "hesitation" when playing, especially on maps with unlimited sky. Tomb Raider is hitting 58 FPS @ 2k at the high setting; I'd like to know how BareFeats is getting 99 FPS with a GTX 980 ti.
From my point of view, I'm having a hard time justifying my continued support of the macOS.