About double, which makes sense as each car carries about half the number of passengers. For Beijing-Xian on the T75, regular soft-sleeper is RMB400/417. Deluxe is 710/740. On the Z19 or T43, regular is 424/442; deluxe 782/816. First price is upper berth, second lower.

The price difference, I believe, is due to different routing. T75 takes the shorter route of 1,200km via Zhengzhou. Z19/T43 takes a 1,275km routing via Taiyuan.

On the Hong Kong-Beijing/Shanghai routes, the difference is smaller. Current discount fare for one-way HK-Beijing is HK$1072 for deluxe, HK$841 for regular.