True, but if you're using Final Cut Pro X, the 970 is going to be slower than the oldest AMD card that support MacOS (It's true)
because, FCPX uses OpenCL (AMD) rather than CUDA (Nvidia). Also about your opinion "The 970 is cheaper and you can buy 2 and SLI them up in Windows", first, ever heard of Crossfire? second, you can't setup SLI in windows, that you CAN ONLY do with AMD cards, for SLI, you need an SLI bridge, and third, yes the 970 is cheaper but if you're doing any kind of video editing on MacOS, you might as well go with team red.
See
https://www.tonymacx86.com/threads/amd-or-nvidia-for-final-cut-pro-x.134155/ for more details