Well, firstly, you should work out what is the net in your pocket spending power after tax and housing. You are a US citizen, which sux because you are subject to global taxation, but you do get breaks for double tax. In addition, you should work out your housing budget. In HK, a lot of execs spend anything from HK$20k-HK$60k, so again depends.
As with any negotiation, you don't have to accept the offer, you can counter offer on the grounds of your market worth based on objective facts like salary trends for your position . Alternatively, you can take a risk by taking a lower monthly salary, compensated by either mandatory of discretionary bonus based on performance.
Good luck!