I've ridden this stretch (Melbourne to Adelaide and return) a couple times... many years ago the Great Ocean Road (Roughly Geelong to Warrnambool approx. 245Km/150Miles) was signposted at 100Km/h (65Mph) now, it is 80Km/h (50Mph) alot of the way (within Victoria) often slower and highly Policed. Midweek is the best time to ride it, except Dec/Jan when there are holiday makers everywhere, as well as slow moving sightseers and caravans. It IS one of the worlds great motorcycling roads, just be aware that it is also one of the most visited parts of Victoria.
Other things to be aware of, it is a coastal road much of the way, weather changes can be sudden, also expect sand on the road surface, blown up from the beaches by offshore winds, the odd rock fall - rare in my experience - but they do happen. And no I am NOT trying to deter anyone from travelling this awesome stretch of road, just trying to make it safer, having lost more than one friend on this road)
Cheers! G.