I agree. If you want a change and a surprise, you can take 312 and 306 from Hof to Steinsholt. The passage from Bø to Notodden is the best part. If you want it shorter, then you go from Skien to Akkerhaugen, then Gvarv and Bø.
Excellent trip with some of my favourite roads. It usually takes me about five and a half to six hours depending on how many stops I make????