Let’s say you could build a motor with a perfectly flat torque curve from 2000-8000rpm, and that the tq value for that entire range was 712ft/lbs.
That’s 712ft lbs/271hp@2000....... and 712ft lbs/1084hp@8000.

Hook it up to the OP’s jet drive....... it’s going to max out at 5000rpm....... which would be 712ft lbs/678hp.

However, virtually any power curve that yielded 712ft lbs/678hp@5000........ would also max out at 5000rpm....... unless the upward trajectory of the power curve of the engine was steeper than that of the jet pump load curve, at the point at where the two curves cross.