I'd be willing to bet that this is a standard sized 160kW motor designed for 400V 50Hz, but by connecting it to 480V 60Hz (which will work because the V/Hz ratio is the same), the faster speed increases the mechanical kW rating by 6/5, which comes out to 192kW. But this is insufficient information to determine the motor nameplate FLC, you can only guess, albeit with hand-grenade accuracy.
Wire size is NOT determined by FLC however, it is determined by the charts in article 430, which are based solely on HP. Because of that, the calculated 257HP relegates you to use conductor sizing from the table based upon 300HP, because it is more than 250HP. That's just the way it is. However, when you adjust for voltage drop from there, you may end up in the same place anyway.
OCPD sizing can likely be selected using that hand-grenade guess on FLC of 320A, because the sizing rules have quite a bit of fudge in them anyway. If you end up on the ragged edge though, it may mean closer examination.
Given that this is a pump however, I would seriously inquire as to the design criteria used in this. If it is a centrifugal pump, and the 160kW motor size was selected based on flow of the pump at 50Hz motor speed, the increased flow at the new 60Hz motor speed will increase the motor power requirement 173% to 277kW, or roughly 371HP. Your 257HP motor will be seriously over loaded. If they have however restricted the flow from the pump with a valve to be the same as it would have been with the motor running at 50Hz, then it will be fine (until some future fool opens that valve more to get more flow). I've noticed that importers tend to get that little detail wrong quite a bit though, so be careful.
