2560x1440 resolution over HDMI with a laptop with NVIDIA Optimus and Ubuntu 15.10

I attached a new 2560x1440 display (Dell P2416D) with HDMI to my dual-booting laptop (Asus N56VJ) that has NVIDIA's dual-GPU technology. In Windows 8.1 I got the display to run with its native resolution and 60 Hz refresh rate by creating a custom resolution in NVIDIA settings. The display menu also shows that it is running 2560x1440 @ 60 Hz, so no downscaling is involved. However, in Ubuntu 15.10 I have had no luck enabling the native resolution. The display settings widget is only offering picture sizes up to 2048x1152, and running Xrandr fails in the following way: fabio@fabio-N56VJ:~$ xrandr --newmode 2560x1440 311.825 2560 2744 3024 3488 1440 1441 1444 1490 +hsync +vsync fabio@fabio-N56VJ:~$ xrandr --addmode HDMI-0 2560x1440 X Error of failed request: BadMatch (invalid parameter attributes) Major opcode of failed request: 140 (RANDR) Minor opcode of failed request: 18 (RRAddOutputMode) Serial number of failed request: 36 Current serial number in output stream: 37 I have tried modelines generated by the gtf tool, and ones based on Windows settings exported by PowerStrip. I am running the latest NVIDIA binary drivers available in Ubuntu, meaning nvidia-352. My HDMI cable supports specification version 1.4, too, although that should not be the problem since display is running fine on Windows. Is there a way I could force X.org or Xrandr to force set the mode, or another way to get to use the display without scaling?