Perhaps you could explain in more detail?
I accept that the numbers say that a P8 is bigger than a Nimrod and P3, but from experience of operating in the 3 different airframes, the P3 has a much more spacious feel about it, and certainly for the pilots, the flight deck is much more spacious and comfortable.
I guess it all depends on the mission equipment layout and internal design as to how cramped the inside feels when flying for long periods.
Before anyone suggests it, I have no experience of operating a P8, but yes to operating a military 737NG.
Y_G