Verified answer

You can't. 1/200th is the maximum on your camera for syncing with the flash.

It doesn't matter any way. The flash goes off faster than that.

First, there is no way for you to do hi-speed sync with the A.B's. This function is calculated between the on-board computer and a dedicated flash that syncs up with that same computer. As far as all the calculations for f-stops and shutter speed, they can't be guessed in advance because the conditions are an unknown and very different in sunlight as opposed to a subdued light studio. F-stops and sync speed are irrelevant when using a flash and the only issues are ambient light and depth of field. A flash freezes the action whether you are at 1/60th or 1/250th. The lower the shutter speed the more ambient light is going to come in so in this circumstance slower is not necessarily a bad thing. The flash is closer to your subject than the sun is and the light from the flash unit will win out as far as lighting your subject goes. Using flash outdoors is a matter of balancing flash against natural light and the simplest answer to this question is not to over complicate the solution. As long as you are not trying to overpower the sun, the A.B. is probably not necessary. I just had this circumstance come up a couple of months ago when I did an outdoor drill team shoot on a bright sunny day. ...I let the camera figure it out for me. I synchronized my camera to the flash and set it on aperture priority and shot at f2.8 with my flash on a stand with a shoot through umbrella camera left about 6 feet away and up 45 degrees. The shots were all money, just enough ambient light, a blurred background and no harshness. The fastest shutter speed on my shots was 1/125th at f2.8. Get either the wireless commander or a long flash extension cord so the flash will work dedicated, put the flash on a stand or have someone hold it, shoot aperture priority at your preferred aperture and let the camera figure the rest out for you. The results will surprise you in a good way. Again shooting outside is completely different than in a studio, you're not lighting a scene, your balancing with ambient and because it's closer, the flash will win ...unless you are shooting directly at the sun. I would practice, you have plenty of time before the big day.

High Speed Synchronisation