PVG has been a 3 day, but I don't think PEK has been since 117 went into effect.

With the acclimation that the longer layover gets, you have 4 hours of "headroom" when departing PEK.

With the shorter layover that you have in PVG, you only have 1.5 hours of "headroom" on departure there.

If you had the shorter layover in PEK, then your duty limit would be shorter and you would go from the 4 hours of headroom down to 2 hours (shorter flight back to ORD from PEK than it is from PVG).

Unfortunately, due to the above mentioned taxi out delays historically in PEK, the company doesn't want to take the risk. My personal experience is that it has gotten substantially better in PEK, but I am not sure what the current data shows and it may just be that I have gotten lucky.

Apparently the data shows that PVG is enough better than PEK that, even though it is a longer flight, it can still be done as a three day. Hopefully my personal experience is actually becoming reality for PEK on a daily basis and we can get the trip built as a 3 day.