I've had the fortune to go on yet another getaway to the not-so-distant country of Spain, where conventional lines use the Iberian gauge of 5' 5-21/32''. Although it was devoid of any long-distance train trips, I still had the pleasure of experiencing the suburban Cercanías service in Madrid.
The Class 446, De Hugh Llewelyn - 180 Uploaded by Oxyman, CC BY-SA 2.0, Enlace
The Renfe Series 446 and 447 make up a portion the current Cercanías fleet. Since they look almost identical from the outside, I'm lumping them together in this post. In reality, though, the two series differ considerably mechanically.
In a nutshell, the Series 447 is lighter and faster. They have more modern electric motors that help them accelerate more rapidly (more details on Class 446 here and Class 447 here).
The two series are compatible in multiple-unit, if necessary, and up to 4 sets can be coupled together at a time.