It depends on the time of day & which rail station. BJ south & SH are mega stations to avoid at rush hour. I have only taken D & G trains & have not seen any 'day' porters, but i do know some people hire helpers for a few rmb to assist with luggage. In BJ, its only 2 rmb for a platform only rail ticket, very worthy...

Be prepared for taking a stairs, sometimes the escalators do not work...

On the D & G trains there is a spot at the end of the car for large luggage, also there is quite abet of leg room on most trains between the seats for a small bags when the 'open' overhead is full. the HSR overheads are only about 16 " deep.

I used to use a standard 15 X 22 " rollerboard and a large dell computer bag. It was tooo much.( stairs, people etc. ) So i bought a new 15 X 22 " rollerboard with an exterior computer bag slot so as to have just one piece of luggage, then i can use my elbow & forearm to navigate the people chaos.

Lots of gate lice in china with any type of transportation.