Being a German and knowing the traffic here, I can hardly imagine what should be fun about driving on those crowded German Autobahnen. Perhaps at 4 a.m. in the morning when there is little traffic around... Well, anyway, if you like it...
To enjoy the scenery, country roads are much better.

Don't go on a Saturday. Most holiday accommodations in the Alps and Italy change their occupants on Saturdays, which means that there will be thousands and thousands of travelling tourists queueing up on the highways around München.