ADuCM350 highest freq range


I am working on the aducm350 eval board and I wanted to know the highest freq I can code in it for the 2 wire bioimpedance sampling.

I am using 2/4 wire config, without the iso capacitors.

I wanted to use this chip for the bioimpedance spectroscopy and hence I wanted to know how high can I go in terms of "frequency" of sampling. If I understand correctly, the highest I can go is the 78kHz? But I tried even higher frequencies and sometimes there was reading out of DFT and sometimes not. If someone could shed some light on this?