Using a notebook with HDMI 1.4 output and Dell U2711 monitor is a bit tricky, the monitor EDID info claims to be able to support resolutions up to 1920x1080 only.
Trial and error showed that I can override it using xrandr (note that frequency is only 40, any higher and monitor just goes blank):
xrandr --newmode "2560x1440_40.00" 201.00 2560 2720 2984 3408 1440 1443 1448 1476 -hsync +vsync
xrandr --addmode HDMI1 "2560x1440_40.00"
xrandr --output HDMI1 --mode 2560x1440_40.00
https://wiki.ubuntu.com/X/Config/Resolution was pretty helpful in figuring this out, it's a bit less helpful in figuring out how to set this permanently.
Seems like best way is to include it in /etc/X11/xorg.conf but that is a bit tricky since I don't always use this monitor (computer is a notbook), I only want a new modeline to be applied everytime I connect the monitor.
Essentially I would like to override the EDID, it almost look like I should look into udev or something, not X windows.
I also see there are some settings conditionally applied (MatchProduct) but that only seems to be used for input devices.
Some people also recommend ~/.xprofile or ~/.xsession but that seems to be executed a bit late in the startup process plus these are not executed anymore. Even if they were still executed, I want the new mode set whenever I connect the monitor (might not be connected during startup).
Any recommendations on how to best accomplish this?