FWIW, there have been times when you could buy with a 30% deposit and have 20 year P+I mortgages with lower payments than rent. For a short period there were developers offering 2nd mortgages for 25% on payment free terms for the first 4 years - meaning you only had to put down a 5% deposit.
I would be surprised if you could get positive cash flow on a 40% or 50% deposit these days. But as long as the double stamp duty is in place I have no interest in buying again for investment purposes.
If buying for home use, given the very high transaction costs, I would need to be very confident that I would be living in Hong Kong for a good number of years to be tempted.