It's not possible to use the tail-sync technique without noticeable fading of the brightness from bottom to top of the frame. The precise result depends on the flash duration (mostly) and camera type and trigger (partly) and varies from acceptable, to totally useless - the longer the flash duration the better.
And there is always very substantial loss of brightness/exposure, the higher the shutter speed the greater the loss. The t.1 time is a factor, but much more significant is how much of the frame is uncovered at any one time. At 1/8000sec you'll only be getting a tiny fraction of the total light output - at that speed, the slit in the focal plane shutter is only about 1mm. In reality, at faster shutter speeds in the thousanths, the loss of brightness is several stops and more.