Going through centro was not as big a problem as we thought it was going to be. There was a Trafico Pesado sign to the periferico so I assumed we weren't supposed to be going through town, though there were a few dually dump and delivery trucks along the way. We made it through with out getting stopped.
Here is a link to the appropriate
blog page. of last years trip. (a Saturday)
We have also driven most of the southern part of periferico in the Tracker some years ago. at that time it was quite doable in a motorhome but then so was the northern route!
Note that the GPS was sometimes shaded by trees and/or buildings and was frequently a bit behind.