I have 29" Wide monitor (21:9). I usually have 2 programs on it side by side. I use keyboard shortcut Super+Left/Right.
It works great except I would prefer to split screen 60-40 not 50-50 (or maybe 70-30, it will need some testing). The reason is one of the programs is code editpor for which I need quite a lot of room (but not whole screen) and the other is Chrome (or Firefox) Developer Tools, for which I don't need so much space.
I am on Ubuntu 17.10 and using multiple (4) desktops and 2 monitors, but I think it is not relevant.
Thanks a lot.
You didn't ask a question, but as to whether it's possible to achieve a 60-40 split with a keyboard command in a default configuration, the answer is no.
You could hack something together, but it might be easier just to grab and drag the window borders like usual. To speed this up, make the window borders thicker.
If you're on KDE, you have more options. There's a command called "Pack Window to the Left" to which you can assign a global shortcut under global shortcuts. Depending on your application, it may help do the trick even faster.
If it's always the same two programs, you get even more options: go into KDE's Special WIndow Settings for that window (right-click the title bar -> More Actions) and you get set the default dimensions, location, and much more, of the respective window.