My info says that the P-61B tops out at 366mph, well below the P-38L's 414mph.
The P-61C has a top speed listed as 430mph, but I understand that the C was too late for WWII.
P-61B Black Widow
Top Speed: 366mph
Initial Climb: 2,200ft per minute
Service Ceiling: 33,000ft
Range with maximum fuel: 2,800 miles
Width: 66ft
Length: 49ft 7in
Height: 14ft 8in
Empty Weight: 24,000lbs
Maximum Takeoff Weight: 38,000lbs
Armament: 4 M-2 20mm cannon fixed forward and a dorsal turret with 4 .50 calibre machine guns.
Ordinance: 6,400lbs of external stores.
I think that it would be a neat aircraft to have even in a daylight context.
I don't think it stands out as a particularly stunning night fighter however. It is a bit slow for intruder work.