Stuffy
What is not understood about endurance ?
Well, at first glance,
we seem to understand it better than
you 
Of course, a lot will depend upon your requirement. If your platform, or platforms, meet or exceed your requirement then you have your solution/options.
This from QBF's linked report on IOT&E:
P-8A aircraft flight performance meets or exceeds operational requirements and fully supports execution of the ASW, ASuW, and ISR concept of operations. The system provides increased range, payload, and speed compared to the legacy P-3C aircraft.
So it would seem that the jet-powered P-8 is able to meet the required criteria and exceed that of the turboprop-powered P3. How that translates to endurance will of course depend upon a number of factors.