Just called again and another agent quoted me 195K miles/person if I include CZ in my itinerary. She transferred me to rate desk's agent who told me that extra 45K skymiles are required because china southern has special dates on which you cannot combine them with another DL flights at low mileage. Aka blackout dates. Since I'm looking for new year 2014 travel, sure enough december 7 - january 6 are forbidden days for CZ.
Is it true? I never heard about such rules.
That's crazy-talk. Either you can redeem for CZ or you can't. There's no way that they can just say you can't combine with DL that I've ever heard of.