Did you look into HKG and MFM in addition to SZX? Both are more convenient wrt Zhongshan IME, but more importantly, you want to give yourself more options. The 90k price looks good to me, but you should be able to include your final leg for that...maybe try calling.

On a semi related note, check out (and maybe subscribe to) the following thread:

Four Airlines to operate Taipei-Seattle

It's a little difficult to predict whether or not all of the new flights will survive until next February, though I give CI better odds than the others.

ETA: It has occurred to me that CI also has flights from LAX and SFO, so you shouldn't have much to worry about in the event SEA gets axed. Just try to optimize your ticket before handing them miles.