I have read that i can use the SB-600 for highspeed water shots. Im using the D70 and i cant figure out how to get to higher shutter speeds. It limits me at about 500, not nearly enough for sharp water shots.
That said one must still overpower the ambient light for this to work. And it is true depending on the flash duration. The SB-800s have a max duration of 1/1000th but my camera can go faster than that. Mind you it's not like at 1/8000th I can get a full blast from the flash. The strobe effect in auto FP mode takes a bit of power from the flash.
You need to set your camera's max sync speed in it's custom menu somewhere. Check the manual for where but I guess the option will be somewhere under the Ds. It's Max Flash Sync Speed, and set it to 1/250th Auto-FP. The flash should show FP on it's display and it stops blocking your shutter speed.