I looked in some of my Pilot's Operating Handbooks and found the folowing:
I have a 1940 flying manual for the Messerschmitt 110 produced by the RAF, It does not give a variant … just calls it a "Messerschmitt 110." It lists the aircraft limitations, but does not specify whether the speeds are VD or VNE. From the way it is worded, I assume VNE. It lists the maximum permissible indicated speed as 650 kph (406 mph); max IAS with flaps and undercarriage down is 250 kph (155 mph); and best approach speed as determined by RAE pilots is listed as 160 kph (100 mph).
AAF Manual 51-121-5 for the North American P-51 Series D and K lists Max permissible speeds as 505 mph IAS. I take that to be Vne since this is a flying manual, not a design manual.
I have a flight manual supplement for the North American X-15 dated February 1962. It has a rather interesting airspeed limitation chart. Altitudes are pressure altitudes. It goers linearly from about Mach 0.7 at sea level to Mach 1.5 at about 18,000 feet, then jumps over the next thousand feet to about Mach 1.5, then jumps almost linearly to about Mach 2.2 ay 37,000 feet, up to Mach 3 at 39,000 feet, and then goes to Mach 3.5 at 40,000 feet. There is a high permissible Mach if properly configured that can take Mach 3.5 up to about 49,000 feet. Since we KNOW it went way faster than these numbers, I surmise they did so at higher altitudes than 40,000 feet. Mach number is true Mach number. The record is 4,519 mph (7,274 kph) set by Pete Knight on 3 Oct 1967, but his altitude is not given with the speed record. I seem recall it was over 60,000 feet. If you use 761 mph as Mach 1, then Pete went Mach 5.94. I believe q max was something like 2,200 pounds, and I expected a q max for these speeds.
For the Supermarine Spitfire IX and XIV, I have max IAS as 450 mph between sea level and 20,000 feet, 430 mph to 25,000 feet, 390 mph to 30,000 feet, 340 mph to 35,000 feet, 310 mpg above 35,000 feet. Altitudes are pressure altitudes.
For the de Havilland Sea Hornet F.20 I have the following in IAS knots and pressure altitude. Sea level to 10,000 feet – 350 kts, 340 kts to 20,000 feet, 260 kts above 20,000 feet.
For the de Havilland Mosquito FB.6 I show the following in knots IAS when clean (any other configuration is slower). 370 kts to 10,000 feet, 350 kts to 15,000 feet, 320 kts to 20,000 feet, 295 kts to 25,000 feet, 260 kts to 30,000 feet, and 235 kts to 35,000 feet. No indication whether the altitudes are pressure altitude or indicated altitude. Since most of the rest are pressure altitudes, I'd assume that unless I could confirm it otherwise.
For the Hawker Sea Fury 10 and 11 I have the following in knots and pressure altitudes when the aircraft is clean (slower if carrying stores). 425 kts below 10,000 feet, 385 kts to 15,000 feet, 355 kts to 20,000 feet, 320 kts to 25,000 feet, 285 kts to 30,000 feet, 255 kts to 35,000 feet.
For the Grumman F6F Hellcat I have 415 knots IAS for the F6F-3 and 430 knots IAS for the F6F-5, all altitudes. Grumman tended to make things very strong rather than design just for the requirements.
For the Northrop P-61 Black Widow I show an unusual airspeed indicator and limitation, It has a moving redline and will be at either 430 mph IAS or Mach 0.7, whichever is less, regardless of altitude. Better hope the ASI works when you commence diving, huh?
I have a flight manual for a P-4N that shows the max diving speed to be 485 mph IAS regardless of altitude. Seems like it was fairly stout, too. I know our P-40N is built like a tank.
For the Bell P-39Q Airacobra I show a max permitted dive speed of 523 mph IAS but a max recommended dive speed of 475 mph IAS, regardless of altitude. The manual strongly recommends starting your pullout from a dive at 10,000 feet to avoid overstressing the aircraft. That sort takes the starch out of a diving attack from 3,000 feet, doesn't it?
Never heard of a Wildcat, Hellcat, P-39, P-40, or P-61 that was thought to have been a weak airframe. They may had had some issues along the way, but not enough strength wasn't one of them.