I just bought a 8,200mi e90 2011 335i xdrive not CPO'd, but more options:
M-sport, convenience, and cold weather packages
navigation, ipod, auto high beams, premium sound, sat radio
I'm guessing my added options would offset the CPO value. Bought it for $44,500. I think you still have some negotiating room in there. Try offering $43,000 or so.