Some banks are more aggressive than others, so if you are seeking a bank that will maximize its lending to you, it is worth shopping around a little. Some banks may be more flexible, such that if you need, say a 10% larger valuation they might extend this to you.
Also, almost all the banks lag around 2 months behind the market, as they base their valuations on recorded transactions.
Finally, in a rising market, buyers, at least historically have paid 10-15% “above bank val”. My feeling is that for now, the rule of thumb is bank val +5%, though this may rise if the market heats up again.
Some useful links for HK bank valuations below:
Bank of China property valuation
HSBC property valuation
Standard Chartered Bank property valuation
Hang Seng property valuation
Wing Lung bank property valuation