well, I doon't know the exact detail specification difference, but that's the anwer I got from KW Germany last year. If you call KW USA, these people in the technical support are clueless as they refer all my questions back to KW Germany. Therefore, you will have to go direct to H.O.
If you like, you can contact KW yourself to get more detail & explanation. I know when KW terminated their V3 for Xdrive, one of the online vendor told me CKS was interested in doing a pilot project of coilovers for the Xdrive but they have nothing to go on except possibly trial & error type of experiement.