Dave: Yes, I read a very good technical article on the compressibility problem in the P-47 in a historian magazine a few years back.

Air and Space ran a double pgae plus poster of that long Chrysler engine in the P-47 a few years ago.

The XP-47J was not as pretty but it hit 505 MPH.

But the Ultimate Jug was the P-72. Oh, Lord, what a gorgeous airplane! An R-4360 up front and if it had gone into production they would have used the P-47N airframe. 500 MPH plus would have been no problem.