If you want a good clear run on GOR (irrespective of time of year really as it's always crowded... but worse in summer) you need to leave Melbourne by 5am... It's a long day if you go all the way to the apostles so it's not really a bad thing to leave at that time.
I can highly recommend the Targa High Country roads around Mt Buller / Mansfield area. The Reefton Spur and the roads around that region are worth a drive too. The Black Spur is the best known road around there and is a great road, but too much traffic... There are quite a few less well known roads around there which are worth a drive

The thing you'll love about the roads down here is that the speed limits are typically more realistic than they are in NSW, so you can actually have a lot of fun without doing anything (too) illegal.