Cheapest (efficient/silent) dedicated GPU with native Mojave Support?

Hi lovely people,

I'm looking to get a dedicated GPU to use it instead of my UHD 630 iGPU.
While the UHD 630 works fine, I'm experiencing some framedrops on 4K on heavy animations from now and then.
Totally alright, but still room to improve (coming from High Sierra with a Nvidia 1070TI).

While GPU Buysers Guide is a great place to start my research, It doesn't really tell me about the sweetspot between:

- Price (used)
- Compatiblity (native on Mojave, Catalina)
- Efficiency/Noise (Fan stop, passive cooling, ...)

All I need the GPU for is a smooth MacOS experience on two 4K screens, no heavy rendering or gaming. I would imagine this use-case is pretty common.

I do you have any advice?

Thanks :-)

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Right now I'm looking at a MSI AMD R7 260X in my neighbourhood (25$). Go for it or get something newer like a RX 460?

Thanks a lot