Dax: That's great if you want to wake up at 3 AM (east coast) to start the day. The question was for the asian markets so i'll stick to that. But yes, IB offers it, check out the web site for details.
SPI: We don't support the overnight sessions at this time. They aren't very liquid and we haven't had much demand.
Correlations: SPI, not great. The Share Price Index is heavily weighted with natural resource companies and thus any bad news in the US which could drive stocks like news corp lower is often offset by moves in those companies (and vice versa).
Hong Kong: there is a pretty good correlation to the US markets. I.e. a big overnight move in the states usually leads to a strong opening. However, the last two weeks it seems that large overnight moves in the Hang Seng have led the large moves in the states. (could be a reflection of news occurring after hours in the states).
SPI cash: I'll see if I can get it added.
Quotes: IB's quotes are direct from the API's at the exchange. Our feed is faster than the major data providers. Our prop side trades off of these feeds and I can attest that they are excellent.
Japan: what I mean by institutional is that it tends to be driven by large orders and/or news that you'll be the last to find out. However, it definitely does trend.
Fees: IB has the same philosophy overseas as it does in the states. For HK we charge 41.5 HK per HSI trade (17 for the mini) which includes all exchange and gov't fees. I do not know of any brokers offering lower fees. For SPI: 7.95 AUD, ditto includes all fees including 10% GST and I do not know of a cheaper broker for those trading small size.