best gpu for vray and view ports

[afshinmp]

dear

I looking for to improve my gpu in 3ds max and vray but I am really mixed up.

I am using 1080gtx but I wanna improve my gpu for vray gpu rendering and smoothing in view ports.

i have 3 thing to do.

1. use 1080 gtx in sli (2x1080) does 3ds max and vray know SLI?

2. chose 1080 ti.

3.useing p5000.

please help me to chose right chose.

thanks.