Hi,
for a level translator there is no such thing as "data rate".
The "data" transmitted may be RZ, NRZ, or maybe any other.
And for designing the circuit, you don´t need the data rate of the translator either.
All you need to care for usually are "setup" and "hold" timings of the according interface.
And thus you only need to know the delay (and it´s uncertainty) of the translator. (besides the already known ICs).
And this informaton is already given on the first page of the translator´s datsheet: less than 1.5ns propagation delay.
For sure you should have a look for more details at the following pages.
Klaus