One thing worth keeping in mind when planning drives in Hokkaido is that the speed limits are absurdly low. Regular highways are 50 km/h, including places like Tokachi where the scenery is flat and you get 20+ km stretches of wide and absolutely straight roads, and even the Doto Expressway has a speed limit of 70 km/h. Because of this, most locals drive a good 20 km/h above the limit, even 30+ on highways, but police do occasionally stop and fine people pretty heavily.

TL;DR, in Australia you can drive 300-400 km without breaking sweat in 3-4 hours, in Hokkaido you'll only travel 150 km -- possibly less if you get on the twisty little mountain roads, where the speed limit is 40 km/h and you really don't want to go much faster!