Join a DayZ experimental 0.61 server. Notice that there is no choise to change the render resoloution, which is possible on the stable version.
Go to Documents\Dayz and open the DayZ.cfg file. Changing "Render_W" and "Render_H" to a higher value than you have set on "Resolution_W" and "Resolution_H" will cause a mouse-delay in-game. Changing "Render_W" and "Render_H" so it matches your resolution on "Resolution_W" and "Resolution_H" will fix the mouse-delay issue.