Fastest piston fighter

Yes, absolutely. Just look at the Thach Weave, a tactic ace Jimmy Thach invented in which two somewhat inferior Grumman Wildcats could be used to kill a more manouverable Zero.

Or the Me109 using the "bunt" or start of a dive to get rid of a pursuing Spitfire. 109 was fuel-injected and its performance even, regardless of manouvre. Spitfire was carburetted and would momentarily starve if gravity were affected by centrifugal force.

We are talking TAS or groundspeed, definitely not indicated airspeed. None of the aircraft mentioned, with the possible exception of Rare Bear (the Reno racer converted Bearcat) could go anywhere near their top speed at sea level. The top speeds you see qouted for almost all aircraft, except un-turbocharged/supercharged piston engine aircraft, are always achieved at higher altitudes, so the indicated airspeeds are much lower than true, and much lower than the top speeds quoted in the books.

WHen I was flying F-5s back in the 80s I would routinely cruise at 0.95 mack on cross country flights, but the indicated airspeed would generally be below 300 knots at the altitudes I was flying (usually high 40s). In B-52s I would see 240knots when flying at out typocal cruise speed of .77 mach in the high 40s. A WW2 P-51 (not a Reno air race prepped one) could only go about 250 knots indicated in level flight. It's quoted top speed of about 440 mph was achieved in the mid 20,000 foot range I believe (maybe even higher) and the pilot probably only saw around 250 on the airspeed indicator.

COme to think of it the structural limiting airspeed of the entire F-5/T-38 series of jet fighters/trainer, was 710 knots indicated. But the F-5E could go mach 1.6 (over 1,000mph). The fastest mach number I ever remember seeing in an F-5 was about 1.3, but the indicated airspeed was only about 350 knots if I remember correctly (in the mid 30,000ft range). The structural limiting airspeed of many civil jets is only in the high 200 to low 300 knot range, yet these aircraft normally cruise in the .75 - .8 mach range, though at 30- 40 thousand feet. Even an F-15 has a limiting airspeed of 800 knots, but the top speed is 1650knots if I remember correctly. Virtually all of the very fast fighters of the past 40-50 years has top speeds of about mach 1.2 at low altitude, well below their absolute top speeds that we see quoted. The point of all this is that most aircraft cannot go their top speed, even in a dive, at low altitudes.

The Vought XF5U would have been an interesting candidate for the fastest piston powered fighter.

But its development at the end of WWII and during the dawn of the jet age made it no longer relevant, so it never was fully tested or put into production.

If it had ever reached the predicted specified max of 550MPH, that would have been impressive for a piston aircraft. But it's just one of those odd WWII era projects that never got going.