I created a custom 65hz 1600x900 refresh rate with CVT 1.2 and set it with XRandR. The screen flickers when setting it but glxgears it still shows the vsynced frame rate as 60fps instead of 65.
XRandR shows the monitor is running at 65hz. Monitor is laptop internal LVDS screen and pixel clock limit is not exceeded.
I also tried creating a EDID with the custom refresh rate using
drm_kms_helper.edid_firmware and it made the boot screens run at the refresh rate but when the greeter is started the screen flickers and is set back to 60hz (I tested with 10hz so I can see the lag clearly and later tried 65hz)
I also tried TestUFO motion tests using Chromium and they also showed 60fps.
Kubuntu 17.04 and GPU is Radeon HD 7640G with padoka / xorg edgers drivers.
Modeline "1600x900_65.00_rb" 106.74 1600 1648 1680 1760 900 923 928 934 +hsync -vsync
xrandr --newmode "1600x900_65.00_rb" 106.74 1600 1648 1680 1760 900 923 928 934 +hsync -vsync xrandr --addmode LVDS 1600x900_65.00_rb xrandr --output LVDS --mode 1600x900_65.00_rb --verbose
glxgears still shows 60fps