Designer/test pilots?
 

Can anybody come up with any designer/engineer of relatively high-performance modern aircraft--i.e. World War II and newer--who was also a competent test pilot?

As far as I know, Kurt Tank is alone in that regard, but I want to make sure before I commit that to print.

Anthony Fokker was too early; it would be hard to say that Igor Sikorsky flew "high-performance modern aircraft"; Geoffrey de Havilland Jr. was not a designer; and even Burt Rutan, though a skilled pilot before he lost his medical, wouldn't have test-flown his company's truly high-performance aircraft.

Am I missing anybody?

Harald Penrose started as an aeronautical engineer and certainly designed / contributed to the design of several 1930's pre-WW2 aircraft before becoming Westland's Chief Test Pilot.

Might be worth checking if he fulfilled your criteria viz. engineering!

SD

Penrose's auto biography [No Echo in the Sky] is a "must read" :ok:

Howard Hughes
 

Barely fits into your time frame, but Howard Hughes was both.

No Echo in the Sky is a good book by him, but is autobiography is called "Adventure with Fate"

SD

I had thought of Howard Hughes as well. And wasn't Phil Condit, who rose from a design engineer to be Chairman of Boeing also a test pilot ? He was certainly a PPL as soon as he could be, even before he went to university, and is an all-round aviation buff as well. Do I recall he has his own Pitts or similar ? Led much 747 design work, and, just on the side, he ran the 727 sales during the years that it became dominant. If you're reading this Phil, in your well-earned retirement, Hi ! Bet the 787 wouldn't have been 3 years late if you were still there.

Actually, Howard Hughes was a famously bad pilot, if you read Kelly Johnson's account of flying with him in a Constellation, and of course he did total that big recon twin the one time he "tested" it. I get the impression, from a considerable amount I've read about him, that he was more a rich guy with lots of airplanes available to him than he was a truly skilled pilot.

Captain Eric ‘Winkle’ Brown, who interrogated Germany’s top aircraft designers and test pilots said in a recent interview that, of all the designers, it was Kurt Tank who impressed him most: "Not only was he Focke Wulf’s chief designer, he was their assistant chief test pilot. I think when you have that, you’re away.”

Not a designer in the sense of the total aircraft, but John Wilson became the chief flight operations designer at Hatfield after a test flying career which included the DH 108, 110, Vampire, Comet (co pilot on the first flight), and Trident.
John was involved with the Trident autoland and flight deck systems design, then very active with the flight deck / aircraft systems in the HS 125 and BAe 146 aircraft; and I suspect with some significant advice on Concorde and Airbus designs via Bristol and Weybridge.

Although he did not design high performance WW2 planes, Toni LeVier did design the Cosmic Wind series of Goodyear racers shortly after the war. And he was the testpilot to make the first flight of a couple of Lockeed designs including the F-104 Starfighter.