Originally Posted by greene

I recently took 8 legs like this in Europe using miles. I recommend you buy advanced seat assignments.
PS The dimensions of European carry on luggage are roughly 2/3 the size of American carriers and weigh limits are often 8 kg.
We ended up checking in our carry ons for this reason.

Originally Posted by findark

As long as you look confident and have a not-overstuffed US carryon you should be fine. I've never been stopped in a few dozen Europe segments carrying a ~11kg 22" bag. But I do agree, be prepared to check if you get weighed.