Which model you have?
With 1080ti founder edition i get 55/56MH on signatum with OC to 250MHz
With 1080ti gigabyte gaming i get about 50MH i can't overclock too much just 150MHz
I don't know why the gigabyte model i can't overclock more.
4 x MSI GTX1080Ti Gaming X
2 x Gigabyte Aorus GTX1080Ti
I have different setup for each card in MSI afterburner:
Powerlimit 82-84
Temp limit 70
GPU core :+120-150
Memory: -500
FAN: 80-85%
I use
https://github.com/tpruvot/ccminer/releases