Well, spanks the P-3 bubbas at least. Have you heard about the "XP-1?"
Kawasaki Heavy Industries (KHI) P-X — Specification
- Crew: Flight:2 Mission:(N/A)
- Length: 38 m (124 ft 8 in)
- Wingspan: 35 m (114 ft 8 in)
- Height: 12 m (39 ft 4 in)
- Powerplant: 4× IHI F7-10 , 13,500 lbs (60 kN) each
- Cruise speed: 833 km/h (450 knots, 516 mph)
- Range: 8,000 km (4,320 nm, 4,970 mi)
- Service ceiling: 44,200 ft (13,520 m)
- Bombs: 20,000+ lb (9,000+ kg)
- Missiles: AGM-84 Harpoon, ASM-1C, AGM-65 Maverick
- Sonobuoys: 30+ Pre-loaded, 70+ Deployable from inside
- Other: MK-46 and Type 97 and new(GRX-5) torpedoes, mines, depth charges
Four engines are nice. Let's compare to the P-8A estimate...
Boeing P-8A Poseidon (MMA Project ) — Specifications
US Navy Fact File - P-8A  and Boeing P-8A Specifications 
- Crew: Flight:2 Mission:7
- Length: 129 ft 6 in (39.47 m)
- Wingspan: 117 ft 2 in (35.72 m)
- Height: 42 ft 1 in (12.83 m)
- Empty weight: 138,300 lb (62,730 kg)
- Max takeoff weight: 188,200 lb (85,370 kg)
- Powerplant: 2× CFM International CFM56-7B, 27,000 lbf (120 kN) each
- Maximum speed: 490 kts (907 km/h)
- Cruise speed: 440 kts (815 km/h)
- Service ceiling: 41,000 ft (12,500 m)
Joint missiles, Mines and Torpedoes
Less data for the P-8A, must be because there is yet to be one making a shadow on the ramp - which is a shame being that we know how the P-3s are doing.
There are some interesting quotes to take on board.
 In this the P-X program will be the exact reverse of the P-8A. The latter is a maritime patrol derivative of Boeing’s highly-successful 737 airliner. KHI, in contrast, built a patrol aircraft but may offset development costs by spinning off a future YP-X civilian airliner derivative. Update: The Japanese Ministry of Defence’s Technical Research and Development Institute site refers to the P-X prototype as a “XP-1”.Here too.
 One batch of rivets from a US supplier had not been heat treated. As a result, 10,000 rivets in 161 locations had to be examined. Many of the rivets had to be drilled out and replaced.
In contrast with the case of ballistic missile programs – in which Japanese generally expressed a desire to be a partner with the United States – development of an indigenous P-3 replacement was characterized as having been decided officially, with consideration being given to maintaining interoperability with US systems. Japanese believed that the United States had lagged behind Japan in articulating requirements for a P-3 replacement, leading Japan to initiate its own programs independently.
...and it flies!