Hi Mike,
A content strategist from Facebook, Emily Shields (@iheartejs) presented on this at Lavacon in New Orleans last Fall. For example, she would add a six character word to a popup box, and with the high traffic, they could measure differences very quickly (she worked in the Facebook payments area I think). Her presentation was the best one I saw - it had lots of "small change" examples with large impacts - you might want to contact her.
Also I think it's good (and not unusual in the UX field) to test language outside of the design when possible - you can test category options with TreeJack for example, or I've put page copy in front of people in a Word doc form and asked them to highlight what confused them and tell me what questions they had. Small word changes can make a difference in perception and/or in how users interact with anything - a website, a software product, etc.
Best,
Melissa