re: Traveling technology
No doubt there's a lot of technology transfer, cribbing, and even espionage going on. But once you specify a mission precisely in a given technology environment, there's probably only a limited number of designs which will be optimized for it; especially when an exremely successful design proves itself in the field. A lot of WWII fighters were very similar in appearance and performance, I'm thinking particularly of the familiar Mako Shark look of the Spitfire, Bf 109, and Mustang, and of many other less popular and well-known aircraft.