Comment Prior Art (Score 1) 280
On my Mac, 8.1-point Helvitica is more readable, has more leading, and takes up only a tiny bit more space.
With a tweak to your system prefs*, 7-point Helvitica takes up about 2/3 the space and is equally readable.
*Go to System Preferences > Appearance > Turn off text smoothing ..., and change the setting to 4.