@adamz: the 1/5000 is gained by having a stripe of light moving cross the sensor. actually the whole exposure process from top to botton of the sensor takes 1/125 of a second or so -- afaik. that's where the flash synch time comes from, cause the flash fires only briefly. with an exposure time of 1/5000 you would have a single narrow stripe on the sensor exposed by the flash. so even if in any given spot the sensor ist only exposed for 1/5000, the exposure of the bottom pixel and the top pixel are separated by 1/125 sec.
@mb: i was wondering, where those 4 shots/sec come from. of course the mirror flip takes its time. so if you skip any viewfinder throughput or AF metering in between shots, you don't need the flip and could speed things up, possibly. in this case the limit should be imposed either by the the readout time from the sensor or by the actual shutter mechanism (not the mirror) or by the aperture mechanism in the lens -- or something else? in video mode there are 24 pics per second read out, right? so it should be possible to develop a "speed bracketing" function. i'll wait for that.