I can understand the need to maximise TPs etc, but we're talking an internal flight, which, if in Y, will earn trivial amounts of TPs. If possible, I would still do an overnight in PEK (which if the OP hasn't visited, is worth a look anyway) and then the train. I'm less of a fan for the transfer flight unless padded with a long layover, since they may not be on one PNR and PEK is notorious for delays, especially in the summer.

Lack of OW in China is a pain, but pragmatics have to come in at some point. When I need to make internal flights, I just fly CA or MU and forget about accrual. I've known colleagues to fly from PEK-HKG-wherever making a 2hr internal flight into a 10hr+ excursion: no matter how nice the lounges in HKG, that's just madness.

tb