I used my US version of Nexus 5 phone in Europe all summer. I use it in CDMA mode at home, and used GSM/Sims in Europe. At home it says LTE, in europe it said HSPA. I didn't notice slow data - it was plenty for what I used it for. (Used wifi at our rental apartments - but used maps/transportation apps when out sightseeing, and also on transfer days on the train.)
I have a friend who did the same thing with the MotoG on her trip recently.
I have a friend who did the same thing with the MotoG on her trip recently.