I'd vote for e550. I'm presuming the woman won't care quite as much about the bigger engine in the E63, and the E550 gives you all the bells and whistles of the newer car, plus the body style will likely age better since it's the "current body." I'm also assuming that the E550, at a base price of $56k, will be significantly less than even a 1-year old E63 that had a base price of $87k.