RBF, that's a good exercise, especially in terms of seeing for yourself what sensible margins are. While I understand why instructors stress the need for adequate airspeed, I've found that in real life I spend more time thinking about how SLOW I can safely approach. As you point out, that involves a knowledge of the aircraft loading, conditions etc. While I wouldn't suggest that a 12 hour pilot focus too much on risk management, the reality is that for daily GA ops excess speed is a far greater danger than falling out of the sky, particularly on the marginal strips often encountered in rural Australia.
And yes, even little aircraft can be very humbling in the face of sloppy technique. I still chuckle when my 'big iron' mates hop into my P2002JF. Just as I did on my first circuit, they invariably find that unless they're properly on the minimum or back side of the power curve, they might as well give it away and have another go. We're kind of ready for it in a Lancair or similar but the insult from a puddle jumper is humbling indeed!