Do you know what airport and Terminal are you connecting through in Moscow? I once had a 3 hour connection in Sheremetyevo Terminal F, and that was the worst 3 hours of my life - smelly and dirty toilets, no AC or air circulation in the heat of summer, 1 food vendor offering overpriced and unappetizing deli sandwiches (which btw closes after hours), no FX exchange desk (shops only accepted Rubles and Euros), inadequate signage for connecting flights, lack of seating, etc. I've heard other terminals are better, but you may need a visa to exit the connection area. I would rather take my chances with PEK, even if it means I have to sleep at the airport in case of a missed connection.

Can you take an earlier flight from Kunming to PEK to give yourself ample time in case of delays?