I did 4 to 4S yesterday on an EU to transfer to an out of EU flight. Here's how it works out. Its a friggin' mess. Sign said it would take 25 minutes. Took closer to 40 (and we're fast walkers), and we didn't need to clear inbound customs. First, you have to find the intertrain. There will be a huge line. There was a 10 minute wait between trains. Once you get off of the Train, you must scramble up the one escalator or elevator that 200 people coming off the train are trying to access then go to EU outbound security. where there was a line and only one line for non-EU residents. Long line but moved quickly. Then, if you're travelling to the USA, you have to go all the way to the end of T4S where they have another (minor) queue for a passport check. I think that trying to do that if one is not especially mobile or with a tight connection might be tricky. Usually when you see a "10 minute walk" sign in an European airport, you can read that as 5 minutes. At MAD, 25 minutes, means "25 minutes or MORE if the train is delayed". That being said, the bags made it. And so did we.

My overall view of that transfer yesterday was....who the &*)$ designed this mess? Its a new terminal.