I just about do all my flying international (US-UK-EU), and trying to really maximize what I can get away with for a carry-on, done only to avoid the rapacious charge for having a check-in. It seems that the one big difference between the US & UK-EU is that the US has the 14" (36 cm) limit whereas UK-EU has this as 40 cm (OK, there are airlines like Ryan Air, but I don't see myself using them). It seems that the test that needs to be passed is the cage, which is 22" x 9", and this the 14" is not a constraint.

I just have to believe that since so many folks from UK-EU are flying with their slightly larger carry-on bags in the US (i.e., as part of the total ticket) that airlines always allow this, and at the very worst will ask to check-in the bag at the gate, which would be free even for passengers with a ticket that has no checked bag. Would this be a good assumption?