> If you want to do, e.g. Control-Shift-Arrow to select text, you now have to use even more modifiers.

Or you're using Vim where just hitting v is all it takes.

I definitely wouldn't use an even smaller board than 40%, though - that is basically the lower limit for me where I can still map all keys to positions I'm comfortable with. Lower than that and I'd need to start using multiple modifiers at once for some symbols.