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I can partially answer your question (regarding E640) . I use them both indoors and outdoors and they are great - good power even for outdoor use. They are portable but not as portable as the quadras mentioned above - but again, they are different animals.
As a long time user, I would like to know if you have encountered any issues where you had to take it back to the company for service? I'm asking this cos I'll be transporting them to India, and sending them back to the company for minor frequent problems would be insane.
E640s have the cost advantage, even for replacement parts (flash tubes etc). If you go the Einstein way, then definitely get the cyber commander and the receiver for them - you can control multiple Einsteins from your camera position (plus it has a flash meter built on the back of the transmitter). Paired with the Vagabond Mini, they are pretty good.
Initially, I didn't care about the cyber commander.. It was not in my budget. But then, the more I learnt about it, the more I wanted it. I'm ordering the cyber commander along with the CSXCV transceivers.
For ultimate portability, check out Godox 360 or Cheetah CL 360 - these are 300Ws Barebulb speedlights and run off light weight external battery packs. You can get remote triggers with power control for these as well. For ultimate portability, they would be my first choice.
I saw one of those in a local photography store the other day and was wondering what it was. Will check them out. Thank you.