i always to go the foreign exchange opposite the pacific international hotel....its on the corner of george and campbell street me thinks....i always exchange my $HK there with no commission.
i thought banks charge rates lower than independent foreign exchange centres, and dont they charge commission as well...for banks that is.
i remember exchanging HK$500 at a bank fo australian currency but im not sure whether charge commission as well (this was at st george's bank)
Post Offices are generaslly reasonable with exchange rates and dont do commission....When I was in England abt to come back to Aus i exchanged all my money at post offices and got a great deal - Im pretty sure Aus Post is the same.
But I found that it was better when I went OS to only take a couple of hundred (pounds in my case) and then use a bank card to withdraw more over there - check with your bank - some (like Westpac for example) have agreements with banks worldwide so if you use their ATMs its just like using one of Westpacs in Australia....
(then again using ATMs was really easy for me because I was opening up a bank account in England)