Just wanted to shoot outdoors in Bright sunshine with flash for bride and groom. Sometimes I need about 1/1500 sec Thats the reason for my question.
Your options are:
-get a Phase One camera, Schneider lenses and studio flashes capable to output full power at 1/1600s.
-use a x2 ND filter and double your flash power
-close the aperture by one stop and double your flash power
-use a 24x36 SLR in HSS mode and multiply your flash power by about 12 times (due to the way HSS works, one needs considerably more power)
-get one of the large veil shades from e.g. California Sunbounce and put the subject under it.