Fill-in flash in bright daylight

I am confused. The other day I was at Centre Island taking pictures of friends participating in a dragonboat festival. It was a bright day with a fair amount of sun. I thought I could just connect my SB-800 speedlight to my new D300 and the camera will just know what to do with the flash. Well, all the background of all the shots I took with flash was over-exposed. The highest speed the camera could be cranked up to was 1/320 sec. I could not figure out it could not go higher. I had set the D300 in Aperture Priority mode.

I just re-read an article I wrote in 2008 about using the SB-800 with my D80:

http://photonfarmers.blogspot.com/2008/09/d80-and-sb-800-high-speed-flash-sync.html

In the last paragraph of the article, I said the D80 would not be able to shoot faster than 1/60 sec in Aperture Priority mode with the hotshoe flash on. It would sound like what happened on the island ... except that today, I thought I'd retest the SB-800 with both the D300 and D80 in Aperture Priority mode.

In both cases, with the SB-800 mounted, I pointed the camera at a bright scene that required a high shutter speed of exposure, like 1/2500 sec. I expected the camera shutter speed to be set automatically to 1/60 sec. To my surprise, the shutter speed adjusted appropriately to 1/2500 sec.

I thought, from my earlier 2008 experiment, that the maximum shutter sync speed in Aperture Priority mode is 1/60 sec (if a faster speed is desired, the D80 needed to be in Shutter Priority or Manual mode.) It does not appear to be the case. It worked fine in Aperture Priority. Could a newer firmware I might have upgraded the camera with, allowed for faster shutter sync speeds with the SB-800??

It does not explain what happened at the island though. Maybe I did not set the D300 to sync with the hotshoe flash in FP mode, as I do not recall seeing the "FP" mode on the SB-800 LCD panel. The "FP" mode needs to be turned on for the camera to sync with the SB-800 up to the camera's own maximum shutter speed. It could also be that I did *not* use the SB-800. I might have just used the built-in flash, which I think was limited to 1/320 sec.

In any case, I am now more ready for a wedding in a couple of weeks. I am sure my relatives will want their pictures taken everywhere, so I had better be ready for it.