We did Perugia to the uk in the reverse to your plan.
The Romantiche Strasse (Romantic Road) is a good ride through Bavaria leading through a little Austria and Switzerland leading onto the north side of Lake Como. Stay at lake Como for a night, its lovely!!!
At the start of the Romantiche Strasse you will find Nurburing, and Wunderlich, both worth a visit.
Riding the West coast of italy via Pisa onto Perugia.
We stayed at a nice 18-30s style modern campsite on the outskirts of Perugia and it was great. Perfect in every way, positioned on the edge of a lake.
I hope you mean 4 days to get there, and not total for the trip as its at least 3 days to get to Perugia unless you REALLY hate you bike and bum.
PM if you wanna know any more.