I switched for the smaller size. The MXPE is AWESOME but if I wanted to carry a tablet around and two-hand my device all day long, I have a N7. Phablets are not for me.
Performance wise they are very similar. I am neither a gamer not do I watch videos on my phone during the day, if that makes a difference. I just need my phone so i can be able to stay in contact, stay organized, and stay up to date with information. Oh, and I snap pics of just about everything that i need to remember so I don't have to carry paper around.
Phone audio quality on the 5x is loud and clear. Front facing speaker is passable--not even close in quality to the dual front facing speaker quality of the XX though.
Wanted to love the MXPE as it would be the 3rd Moto X for me, but I found it too big for one handed use and back pocket carry. If size is not an issue, I'd go for the MXPE for the slightly better specs (RAM, screen resolution, speaker sound, curved back for comfort, etc)