November to April would be the best time, as obviously the weather 'windows' last longer than in winter, as well as no icing and usually less wind.
I am a coward when it comes to swimming with Great Whites, so have always gone via the Wilson's Prom - Hogan - Deal - Flinders route. A forced landing on Hogan would probably be survivable, though you wouldn't get to use the aeroplane again. There is a decommissioned strip on Deal Island which may be OK for emergency use. Also the general route is popular in summer for cruising yachts, so a hand held marine band transceiver would be something to consider.
Because even at 9500 feet, there is a small 'wet footprint' on this route - unless you are flying a motor glider. The smaller you can keep it the less stressful you will find flying what is a most spectacular trip.