sounds like $400 savings with china airlines.

What kind of service or experience that would offset $400 in savings are you looking for?

Seat configuration?
Smiley faces of Air attendants?
Extra drinks?
5 Star quality food?

If saving $400 is more important than any of the above...just hop in it and save the money.

If services are more important then get on Korean or Singapore Airlines for the cost of $400.

The decision making looks pretty simple to me.