Teensy 4.0 is pretty much a Teensy 3.2 with 13X greater performance, as it features a 600MHz ARM M7 processor!
Featuring the (presently) fastest microcontroller on the market, Teensy 4.0 more than quadruples the performance of the Teensy 3.6, and more than 6x faster than an ESP32, and still is Arduino IDE-compatible!
It has the same size and shape as the Teensy 3.2, and retains most of the same pin functions too.
As usual, PJRC has broken out a great many features to this chipset:
Power consumption is also very manageable, being about 100mA in normal operation. Additionally, it supports dynamic clock scaling while maintaining proper timing across the peripherals. Serial and sampling rates work properly as you scale the CPU speed.