You can calculate the flight time but not if you are right with the C-rating?

How did you determine the flight time? The motor is a variable load determined by throttle and propeller. 1600w on 4S can draw up to 100A so with 5000mAh you do need at least 20C to keep on with 100A, 50C should work.

But the C-rating is a mistery number and for sure with higher numbers no continious current but only peak currents.