Stuffy, I don't know what they did to the Mk 2 to get an endurance of 10-12 hours unless it was flying round the Moray Firth at endurance. A typical mission was 9 hours and I never exceeded 10. The last bit of gravy was sometimes a MAD Comp or circuits.
The figures you quoted are apples and pears.
Maximum speed:490 knots (907 km/h)Cruise speed:440 kn (815 km/h)Range:1,200 nmi (2,222 km); 4 hours on station (for anti-submarine warfare mission)
The Nimrod was considerably slower - 0.76 Mn in the cruise - so the P8 mission profile you quoted would match that of the Nimrod but with shorter transits thus equating to a sortie length of about 9.30. The Nimrod with a speed of about 400 kts (IIRC) would be 10 hours.