It's the SS583. In the week is not to bad but get's a bit tiresome as you need to concentrate so you don't have much chance to look around. I would avoid at the weekend if the weathers good it becomes a log jam. Especially if you get a couple of coaches passing each other.
Agree the ferry is a nice option to Bellagio.
If you are staying in the area and fancy a nice driving day trip, Bergamo is a pretty city and there is also another lake "lago di Iseo" fairly near. Two main places to visit on this lake "lovere" and "Iseo"
Lake Garda is a nice lake to visit. Sirmione is a must stop on the lake and Verona is near. Verona is well worth a stop. Watch speed around the lakes, the police are always checking and make sure you have your registration, passport and driving license on you.