I agree. I did this trip late August-22. I kept the east side of Tinn to Austbygd and a small road from Rødberg to Haglebu and down Eggedal and Sigdal. This is shorter and more interesting curves for mc.
This is a perfect daytrip, but with over 400 kilometres you need to leave not too late in the day. Approximately 6,5 hours with just pure and fun driving + stop. A lot of places to stop to enjoy the absolutely amazing scenery, and good places to eat as well. This roundtrip will not disapoint you! Enjoy the ride!
Just breath and relax. Imingfjell.