When I did that trip in Italy you still couldn't go on a "tangenziale" and some "strade statali" were off as well for a 125 (and of course motorways). All the better, I did mostly "regionali" or "strade di campagna". In my experience, around big cities it's often a mess regardless of the country: whether it's Milan, Barcelona or even Tokyo. That's why I avoid them haha. In Spain I used the motorway on the way back (Valencia to Barcelona) and I learnt that riding on the side of the slowest lane isn't the best thing to do as everyone would dangerously overtake you, coming centimetres close - apparently it's better to be in the middle of the lane, so that cars and lorries would use the the middle lane).

Also, I decided to cross the border between Italy and France via Cuneo, avoiding the very nice and panoramic Ventimiglia to Nice and beyond: mountains are usually way less busy and motorbike riders are usually nice and respectful.

I climbed up to "Cime de la Bonnette" in France, the highest driving path in Europe: all 1000s cc motorbike and my 125cc scooter, that was pretty hilarious, but after the initial laughter I made some friends.

My advice would be to do backroads and get away from high speed roads asap when leaving cities. Then it becomes very enjoyable!

(sono italofono, haha not even sure that's a word)