Thanks containerstore for answering my question! I've just returned from the aforementioned trip and am following up to share my experience.
I think it would be accurate to say that 1) customer experiences may vary, 2) it is up to the discretion of the screening airline employee to determine what is an acceptable carry-on size and what isn't, 3) as a general rule, smaller U.S. domestic flights will ask you to check this bag, whereas larger international flights won't care (bigger planes = less scrutiny).
My experience: I traveled from Washington, DC to Detroit, MI, then onto Shanghai, China. For the Washington to Detroit flight, which was on a smaller plane, I skipped check-in, but was asked to gate-check this bag, which worked well for me. For the Detroit to Shanghai flight, I carried it on without any problem. Same results on the return trip.
Last comment: I found it helpful to alternate between the handle and the shoulder strap when heavily loaded down, to avoid putting too much strain on shoulders and arms - especially if you have long carries between terminals, etc.
Great bag! Would definitely buy it again. Perfect for two full suits, 4 undershirts, shoes, belt, 4 dress shirts, 4 socks, and a bath bag. Enough for one week anywhere.