Current defaults are from another time. Acceptable defaults could be
common screen resolutions. 1366x768 is apparently the most common
(according to various stats on the web), but since we target advanced
graphics artists, let's go for 1920x1080, which is the second most
common resolution, also known as Full HD.
For unstable builds, let's have at least one odd number, uncommon ratio
and higher values, encouraging tests with less common numbers and bigger
images. I chose 2001x1984. Feel free to update to any other funky values
following these "unstable" rules.