Over here Yamaha and Suzuki are top sellers. Our state alone has over 250,000 registered (licenced) boat owners. There was a short time when some of the modern 2 strokes were popular but soon lost their credebility especially within the commercial sector (police, maritime, fisheries, water taxis, oyster farmers etc etc). Do your home work on those if you get an offer you think good, they don't have the same reputation they get in the UK.
There are a few places in Sydney that sell ex government engines, mostly about 3 years old. These engine tend to of been serviced every 50hrs (I think Buxton marine was one).
When people talk about one engine being a few kg lighter than another I personally don't think this makes hardly any difference at all especially on a 5m+ rib. Nobody seems to consider we are different weight, you might have someone 50kg heavier than someone else. An extra 2 bags of ice in the esky or a couple of dive tanks in the back. I often have a 100lt tank at the back of mine for keeping live bait or collecting fish (under permit) for a south coast equarium.