Lets look at it this way: for the same lens, the same shutter speed, and the same amount of hand shake, but on 2 formats: full frame and 1.6X cropped.
Both systems will generate the same amount of absolute "blurr" on the recording media.
If the final result is the same size, say a 8R print, then the "blurr" on the 1.6x cropped sensor will be magnified more, and thus more noticeable, and thus requires a higher shuttle speed to better cope with hand shake.
I vote for using 1/1.6X focal length. Having said that, it is still just a guide. Your mileage may vary. The shooting situation also affects the choice of shuttle speed. For example:
- you would probably need a higher shutter speed at the end of a long day of shooting compared to when you first started off in the morning.
- you would probably need a higher shutter speed if you are shooting outdoors with strong winds.
- you would probably need a higher shutter speed if you are shooting from a boat sailing on Singapore River
- you would probably need a higher shutter speed when you are excited and breathing more quickly and your heart is pounding harder than usual.
- you would probably need a higher shutter speed than 1/500 sec if you are shooting with a 500mm f/2.8 bazooka lens hand held...(not sure if such a lens exisits, but if it does it is going to be huge)
- you would probably need a higher shutter speed if you have only slept for 2 hours the night before, or if you are shooting under intoxication..a.k.a. drunk shooting
So, don't take this guide too seriously. It is more important to known your own capability in holding the camera steadily.