Electronic flash will sync with leaf shutter at ANY speed, just make sur the flash selector, if there is one, is set to "X". That's one of the advantages of leaf shuuters as opposed to focal plane shutters.
Leaf shutters are great for electronic flash and, as Wayne has said, sync at all speeds. When I was doing weddings many years ago I often used 1/125 for outdoor shots when fill flash was necessary or could improve a picture. Sometimes 1/250 was needed, depending, but 1/125 was fast enough to stop movement in most cases and also permit good fill flash without too much or too little fill.
The technical reason that a leaf shutter can sync with electronic flash at any speed is pretty simple: the shutter opens fully at all speeds so it's only necessary to trip the flash when the blades reach their full open position.
IMO, a 6x7 and a lens with leaf shutter is about as good as it gets until you move up to 4x5 inch film.
But do I use the same f stop (depending on the distance) the my flash says, no matter what shutter speed I use? I plan on using a Sunpak Auto 522. Craig
Not necessarily. In most cases you'll want a ratio that gives contrast to the shot but still opens the shadows some. Therefore, on the shadow side, you'll want less flash than the natural light on the open side. It becomes necessary to have a flash with variable flash levels (Vivitar 285HV for example) or use the correct distance from the subject to get the effect you want. In outdoor light, many auto flashes won't trip as the light level foods the sensor. Then manual flash is required.
Nothing will beat experimenting to learn how to use fill flash. You can also find books in your library or book store that explain things more fully.