The Six was built in the late 50s. It did not have an AOA gauge. The plane had to be flown by "feel" at slow speeds/high AOA. Leaning to fly this machine by "feel", helped me greatly in the F-4. The F-4 did have an AOA indicator, but the lessons learned in the Six helped a lot at slow speeds/High AOA.
The Six was very much ahead of its time.
First, the airframe:
It was a very "clean" design, even with the two 360 gallon external tanks. Most other fighters were a lot less clean. As those other fighters approached Mach 1, parts of the airplanes would start to go transonic at around .9 Mach and the speed would stagnate. That means that you would have to select afterburner (greatly reducing range) to get to, and then through Mach 1. The Six would go all the way to .99 Mach before having to select afterburner. That means the jet would have a 50 to 75 knot speed advantage without afterburner. Before the jet was retired, several speed records were set over the US by the Six because, it was the fastest jet in the world subsonic. Over the US you were not allowed to fly supersonic. Also, many of the modern jets are advertised as Mach 2 capable, but in reality the engines are de-tuned to make them last longer, and the jet is not really capable of Mach 2. You could pick any Six off the line, and it would run Mach 2 (without external tanks) because it was so clean. The aircraft was also the most maneuverable jet in the inventory, at the time, until the F-15 appeared. The F-4 was no competition. Also, the weapons were carried internally like the F-22 and F-35.
The engine was the J-75. It was the same engine used in the F-105 and the U-2 (without afterburner). It was the largest turbojet ever built, and was an outstanding engine in dependability as well as performance.
Weapons system and avionics:
The radar, with its anti-ecm features was the not surpassed until the F-15 appeared. It also had an infared search and track system that has only be used on the F-14 (I think). Other fighters have heat seaking missiles, but no IR search capability.
In the cockpit, the jet had "tape" instruments instead of round gauges (kind of like a modern airliner). It really made instrument flying a lot easier. It also possessed a "data link" system, so radar controllers on the ground could tell you were the target was, and tell you headings and altitudes to fly to get to the target, without any voice commands.
The weakness of the Six was that is was classified as an "interceptor". All the money and modifications went to the F-4 (Vietnam war). It gradually became irrelevant because the interceptor mission went away, and its weapons became obsolete because they were never modified.
Overall, an absolutely outstanding plane that was never allowed to reach its true potential.