i have 2 Einsteins and i find them to be very reliable and built much more solidly than the older AB units. i have not yet tested the high speed flash duration of the units but it was a feature that i liked having if the need ever arises.
some other nice things about the Einsteins:
1/10 stop variation in power over a 9 stop range
ability to control power of multiple strobes via camera with the Cyber Commander unit
value vs quality (its just a good product for the cost compared to other brands)
i have also not had any issues using any type of modifier with them. i got the units when they were first released and i was aware that they were going to correct how modifiers were attached to the unit. as i understood it, occasionally a large/heavy modifier could "jump" off the unit so PCB planned to extend the length of the clasps that engaged the speedring that the modifier was attached to.
i have never had an issue with this and i have used up to a 36x48 softbox on these units. i do hope to get a 54x72 softbox in the future so at that point i might send the units back in to get them updated to handle the extra load.
bottom line is that i find the Einsteins to be well made, reliable, and very very versatile. but i would try to research how they perform at faster flash durations and if they are capable of what you need. the only other units i saw (online) photographers using to do such work were ProFotos...and they are beastly expensive.
just found this review/test by Rob Galbraith (whom i find to be very thorough and informative) for the Einstein 640's. scroll down tne article a bit and you will see interactive tests for the high speed flash duration compared to the elinchroms.http://www.robgalbraith.com/bins/multi_page.asp?cid=7-10053-10715