FormerFlyer
I've never travelled on Air China,but a friend of mine flew to Oz on them a couple of years ago and said they were fine.In flight food was very "chinese"(not your take away variety though...get my drift?!).
Both flights empty,particularly PEK-SYD.
If I was you I'd give it a go.Speaking as an airline employee who has travelled most places on most airlines,on a flight that length,unless you travel business/first,theres not a lot a fat lot of difference.
A stop over in Beijing is a good idea,which is what my friend did.Apart form breaking up the journey,you can visit the Great Wall etc.
Hope this helps.......at least youre not flying on Cubana in April like me!