Titan V on Ubuntu 16.04, which version of CUDA and Cudnn should be the appropriate choice ?

I have get a piece of Titan V.
I test this card on Windows and Ubuntu 16.04 LTS.

I tried: CUDA 9.1, Cudnn 7.1. Driver version of Titan V is 390.

When I using the same DL net and model to do segmentation for a set of images, I find that the Titan V needs more time than 1080Ti (both on Windows and Ubuntu).
So I am wondering whether it is because that I did not install the appropriate version of CUDA and Cudnn ? And which version is the appropriate one?