The go staff at Bintan Club Med told us Harbin could be as low as - 40 c. Furthermore from tripadvisor, there were comments saying that the staff there lacking the service standards of other club med resorts.
I have been to both. Honestly, I think the one in Bintan is much worse.
Harbin is definitely -30 and I wont recommend any young kids to go there.
If you will really ski (v. just walk around and take photos), you in fact wont feel that cold.
During day time, average I think is -10 to -20. Exception is when they have stormy weather....but no one can tell you when they will stormy weather.