Dell xps 13. core i7 skylake with intel hd graphics

Hello everyone !
I am ruing ubuntu 16.04 with keel version 4.4.0. I would like to understand why at my native resolution (3200x1800) most of the UI is sluggish.
When I resize a window, it is considerably laggy for example. I made sure the intel drivers were installed. I tried disabling vsyn. And I managed to fix the screen tearing by adding a conf file.
When I set the resolution at 1920x1080. Everything is smooth, resizing windows is not a problem ( yes this is my benchmark aha ! ).
I find it even weirder that when I tried windows 10 while receiving the machine, everything is so damn smooth.... So I know this is not a hardware issue.

Basically, how do I get the same performance on linux ?
Thank you all !