This is 87 km with a lot of bang for your buck. Exciting, tiny roads that wiggle across the valley sides. It might be easy to brush this route off but it's a great starting point for bigger rides. The climb from Bianzone up to Teglio is included in the Gran Fondo Stelvio Santini but gets so crowded with inept climbers during the gran fondo that it's much better to do in your own time, on your own ride, away from the masses.
There's a section on the Statale that's almost unavoidable, but you could take the Sentiero Valtellina if you really hate the main road.
The route back to Sondrio teases with the 'Via Panoramica', which is delightfully short of traffic and swoops and swerves its way back along the south-facing slopes. It's an exciting route that provides amazing views. There's always the option to stick to the Via Panoramica if you prefer to bypass the super scenic, slightly arduous route that is outlined here.