Just what I was looking for - and it’s free!

My MacBook running Yosemite won’t let me change screen resolution other than the settings “allowed” by System Preferences “Display” (i.e. 1,440 x 900), even the the MacBook screen has 2560x1600 pixels. With this app, I can go beyond Apple’s settings when I need some more screen real estate. Thanks!

Godo Stoyke about Display Menu, v2.2.2