In Ubuntu 16.10 (and maybe older versions too), if you open a terminal window, and go to the
Terminal menu, you can select alternate window sizes directly. In fact, almost exactly the sizes that you are asking for!
F11 will toggle full screen mode.
You can also create multiple profiles that set the screen to exactly the size(s) that you want. Go to the
File menu and choose
New Profile... call it "My editing profile". Then, when you want to change to a different profile, go to the
Terminal menu and choose
Change Profile. Then go to the
Edit menu and choose
Profile Perferences. Set your custom screen size there. Different profiles, each with different screen sizes!