My current flash limits me to 1/200sec whereas that's fine for portraits i'd like something faster around 1/700sec or 1/1000sec so I can freeze fast moving objects like water falling.
When using flash, it is the flash duration, not the shutter speed, that freezes motion.
The actual flash pulse is very short, the maximum shutter speed (ignoring HSS for the moment) - referred to as the maximum synch speed, is actually dependant on your camera, rather than the flash.
The reason for this is the way the camera shutter works, and how high mechanical shutter speeds are achieved.
The shutter consists of 2 'curtains' - you start with the first closed, and the second open.
When you take a shot, the first curtain opens to expose the sensor, then the second curtain closes to stop the exposure.
Since these are mechanical operations, they take time to occur.
For higher shutter speeds, this means that the second curtain actually starts closing before the first curtain has fully opened - so the whole sensor is only partially exposed at any given instant.
The Max synch speed (1/200s in your case) is the maximum speed at which the first curtain is fully open before the second curtain starts to close (plus a small margin).
HSS works by the flash firing a lot of lower power flashes very quickly - so that even though the sensor is never fully exposed, the multiple flashes ensure that the whole sensor sees the scene illuminated by a flash.
The downside of HSS is that while you can have a much higher shutter speed, the flash power has to be significantly reduced (so the flash can fire lots of times very rapidly).