Great post UTR, a couple of my own observations to go along with it.
The Kilmore AWIS is at the North West end of the gap, usually the cloud is higher at that end than down near the sugerloaf/lillydale end, be careful.
Personally 2000-2500 AGL is usually fine to get along the gap, any less and you definitely need to be constantly thinking about escape plans back to Mangalore. Depending on where you are stopping (if at all) fuel may be become something to think about as well. Set check points from Mangalore all the way to Essendon in case (Mangalore, Lillydale and Moorabbin both have fuel).
Generally if you can see the outline of the city from kilmore, you can get through.