I would say 2/3 is "normal" for someone who has practiced bottom-up press enough to get the hang of it, but not so much that they're specializing in it.
24 kg press, 16kg bottom-up press
32kg press, 22kg, maybe 24kg kg bottom-up press
etc.
Someone who practices it a lot might get the bottom-up press as strong as the press. Tracy Cook bottom-up presses 24kg. Harald Motz bottom-up C&P something really heavy... I forget how much but I think >32kg.
It's a great thing to practice! I like to use it as a warm-up for pressing.