Maybe we need some clarification (FOR ME TOO!)
It seems so...
Autovias and autopistas are just the same concept (2-at-least-lanes-in-each-direction roads with a physical separation - not only a painted line -between both directions) and both have the same speed limit, i.e., 120 km/h. Autopistas can be toll roads, but there are free ones, too. The main differences between both are technical (minimum radius of curves, distance between entries, etc...).
The rule that has been recently adopted is to distinguish between toll and free ones by its name: toll ones are AP-something, and free ones are A-something (if they are national, else it takes the first letter from the name of the city where it is, like the M-30 in Madrid). So, we have the A-6 from Madrid to Villalba and, as from this point it becames a toll road, it changes its name to AP-6, until it reaches Adanero, when becames free again, and thus recovers its previous name, A-6, until its end at La Coruña.
The speed limit in carreteras nacionales, depends on the characteristics of the road and it can be 90 or 100 km/h. Most newer carreteras nacionales don't cross the villages, but round them. As long as they are improved, the target is to avoid crossings.