GPU Recommendations

I currently have a GTX 1080 that has been fine for most things but I have seen some issues with larger files in other 3d software and on really large RC constructions the speed will slow down a lot. I have read on here a bit and have seen a bit of varying information on the best set up when it comes to GPU.

What is best?
Keep GTX1080 - Add second GTX1080
Keep GTX1080 - Add GTX1080 Ti
Keep GTX1080 - Add Quadro P5000
Run just a P5000
Remove GTX1080 and replace with 2x GTX 1080 Ti
Buy a P6000 (i will… but i hope this is not the best option)

I have seen mixed things about SLI in RC. I know in a lot of computing aspects and in gaming a single GPU that is more powerful will be beneficial than SLI, but this is not true in most computing aspects. However does having matching cards matter? The biggest thing to look for here is the largest amount of cores and onboard RAM? Very excited to get something more powerful, thanks in advance for any input / guidance.

**** meant to put this in General, not sure what happened :?:

Here it goes forth:
Choosing a GPU

Seen this? https://tinyurl.com/AEC-eGPU

At present, adds a Quadro to an ordinary laptop, external hard drive-style; in future could add multiple GTXs (or whatever’s next) to a gamer laptop