This is an interesting question which I am also looking at. We toured through China on two singles and one tandem for the four of us, so that was 6 rear panniers 2 front and one small trailer but we are in the process of changing to 2 tandems which drastically cuts down on the amount of packing space we have available.
We put our cycle plans on hold after the ISIS attack in Tajikistan but feel confident enough to bring our bicycles over during the summer. The plan will be to run front and rear panniers on each tandem and an "Extra Wheel" trailer which gives us a spare wheel and extra two panniers.