P2414H after OC problem.

[RudiSZT3]

Hi everyone, hi ToastyX!

I've tried to overclock my Dell P2414H to 72Hz. My graphics card is an nVidia GTX 970 with the latest driver (355.82), and I use DP port.
This type of monitor theoretically can handle 72Hz easily.
And it works, but i have some issues.
I tried it with STANDARD TIMINGS and with CUSTOM TIMINGS TOO (with the following values):

Horizontal Active: 1920
Horizontal Front Porch: 30
Horizontal Sync Width: 40
Horizontal Back Porch: 45
Horizontal Total: 2035
Horizontal Sync: +

Vertical Active: 1080
Vertical Front Porch: 3
Vertical Sync Width: 4
Vertical Back Porch: 5
Vertical Total: 1092
Vertical Sync: +

I set the resolution with CRU. If i would like to activate it, i have to choose 72Hz refresh rate (native resolution) in nVidia control panel too.
Then some games (like Crysis 3) works with 72Hz perfectly (VSync set fps to stable 72).
But some apps not. For exaple in Far Cry 4, i can set refresh rate to 72Hz in the garaphics menu of the game, and it works, but i have some frame skipping or something like that (the movement isn't perfectly smooth, there are some jammings all the time (inspite of I have stable 72 fps with Vsync).
In Mass Effect 3, the game set fps to 62 inspite of I've set refresh rate to 72Hz on CRU and nVidia control panel.
When I see http://www.testufo.com/#test=ghosting, it shows, that i have 60Hz and 60 fps, inspite of i set it to 72. There are jammings too.

What can be the problem?