Comment 17 for bug 1606103

So I can confirm that adding the extra modeline works, eg I now have 2560x1440@60 Hz both appearing in xrandr and working on the laptop monitor using the modeset driver.

(There's a separate bug for the modeset driver whereby if you change the mode, eg from 1920x1080 to 2560x1440, the new screen only uses the top 1920x1080 display space - except, curiously, for the unity launcher and top bar - but once I restarted lightdm, the new resolution works fine.)

No, I hadn't heard of quilt before. I'll check it out.