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At full power, they're virtually the same. However, the Einsteins really shine as you go down in power. Their flash duration gets faster, not slower, and the power output has a huge range, which will allow you to shoot studio with almost any aperture, as well as mixing direct and bounced light in sporting events.
I own 8 Elinchrom 600S units, which were considered great monoblock units for sporting events, but after also picking up a 4 pack of Einsteins, I have to say there's no comparison. I've also used and had access to WL and AB's, and previously owned Norman and other lights.
Bottom line: if you want a good long term purchase, get the Einstein, and don't look back.