Prices in Hong Kong

Yes, just about all of the computer parts you buy in HK will be compatible. The only thing you have to watch out for is the Voltage inputs for PSU's, as some local brands only accept a 220V input (as opposed to US 110V inputs)

Generally, Hong Kong prices are pretty much on par with those in the US WITHOUT tax, (i.e. Newegg) but you should sniff around at the three major Computer Centers (Most expensive --> Least Expensive: Wan Chai Computer Center, Mong Kok Computer Center, Sham Shui Po (Golden Computer Arcade + Golden Computer Center))

The current price for a 8800 GT is about 1900 Hong Kong Dollars while a 8800GTS 512 is about 2500-2600: you can find them slightly lower if you look closely at these computer centers, and its possible to bargain with some of the sellers. (very much possible if you pay in cash instead of a credit card)