There are a few variables but a calculator is what's going to get you in the ballpark.
Your RPM is going to depend on your pack voltage, controller, settings, flux weakening, etc. But you can get a pretty good idea from the datasheet.
You didn't specify exactly which motor you're using but I'm assuming its the QS 138 90H. It says it runs at 4000RPM but with flux weakening up to 6500RPM. We can assume these are speeds with no load, and under load RPM will be somewhat lower. I reached out to Electrobraap who used this motor in his pit bike conversion kit, and he said he gets between 5000-5500rpm depending on voltage/current/load.
You can use those numbers and the calculator skaiwerd linked to to gear pretty close to the top speed you're looking for. But you won't know exactly until you build the bike and test it.