I'm running 3840x2160 w/ 6700k OCd to 4.5 and a EVGA 1080 Ti (Factory Overclock), 16GB DDR 3200.
I recently purchased SMP, I really do think it's the best weather addon (I have the other one too). The clouds can come at a cost though.
Flying over a storm through a few cloud layers my FPS can go from 82fps to 22fps in the blink of an eye. In constant weather heavy areas I see my FPS bottom out around 22fps and run in the normal area of 30fps-32fps. The very low FPS is strange as I never see that with my system/ I am a advanced user (developer of 15 years). I watch my sys resources closely, I have plenty of vram headroom (Usually around 4gb)
The 1080ti is a monster and will gobble up 99% of everything you throw at it. Matter of fact - X-Plane and SMP has been it's toughest challenge yet.
I did fly from KDFW to KMIA yesterday, the FPS stated above is the result of that flight.
X-Plane 11 settings are completely maxed out with the exception of AA @ fxaa (First notch in slider).
I upgraded from a gtx 1070 and it is an amazing card. You should be fine with it. Read up on overclocking and learn how to OC effectively and safely. Learn how to do it with confidence before you do it, I don't want my advice causing you trouble :-) The only reason I upgraded to a 1080 Ti is because I fly DCS and il2 in VR and it also helps witht he 4k resolution, otherwise I would have just kept using my 1070.
Also keep in mind that these guys work really hard on SMP and i'm sure we'll see improvements regarding all sorts of things. To be fair though, the clouds look amazing and I don't mind the FPS hit one bit.
My SMP settings are: