Hi Rich,
I would love to say definitively one way or the other, but it's just not possible, there's too many variables. My guess is that your current CPU will be the limiting factor for your framerate, not the GPU processor itself, and as such more GPU performance would be "surplus" (I can only speak for X-Plane here mind, MSFS might be different). However, more VRAM can always be used regardless of your CPU performance, if that makes sense. On the flip side, if you intend to later upgrade the CPU/motherboard and/or monitor (4K), but keep the same GPU then investing in a more powerful GPU now may make more sense. Either way, it's just guesswork as I don't have personal experience with any of the cards you've mentioned, unfortunately.